Snowdon Ordnance surveyors

Index to all Snowdon pages

This page includes:

  • Summary
  • The Trig point
  • The staff on Snowdon visible from Ireland
  • The construction of the cairn 1826-1827
  • 1841 New Survey and Cairn
  • 1886 survey
  • 1937 survey
  • Transcriptions of references in chronological order

Ordnance Survey 6 inch map of Snowdon, surveyed 1886







1802-1820       The first Ordnance Survey of Wales
1803-1809       Mudge reported that ‘The Object [presumably a staff] was placed on the very highest point of this mountain’
1805                Mavor observed a small pile of stones recently thrown up by some artillery-men employed by government;
1806                The base of one side of a surveying triangle was established on Rhuddlan Marsh, 24,515 feet long (7472m, 4.64 miles)
1815-1816        Robert K Dawson’s essay on how to draw topography, included a map of Snowdon
1826                 A trig point on a new cairn on the summit of Snowdon was used to link Wales with the Irish Ordnance survey
1841-1842       The  second survey
1886                 The third survey (for 6 inch maps)
1937                 The forth survey  (using Garnedd Ugain rather than Snowdon)

The Ordnance Survey arrived in Wales in September 1802 soon after which they set up a 4½ mile long base-line on Rhuddlan Marsh. The triangulation of Wales, linking the base line with notable high points, often mountain peaks, was complete by 1811.
A detailed survey of Caernarvonshire was begun in 1816 under the supervision of Robert Dawson at a scale of 2 inches to 1 mile. Dawson’s work is considered to be some of the best cartographical work in Britain and he also produced some fine landscape paintings, but his maps were thought to be more artistic than accurate. In the mid-1810s Dawson’s 18 year-old son, Robert Kearsley Dawson applied for a place in the Royal Engineers and produced a plan of Snowdonia in support of his application.

The trig point
Many of the records of the Ordnance Survey were destroyed during the Second World War and nothing is known to survive to indicate whether they built a trig point on Snowdon for the first survey. However, a list of all trig points in the British Isles and the dates they were first used, dating back to 1792, gives the date of Snowdon as 1842 and the account of the first survey, published in 1811, states that at Snowdon: ‘The Object [presumably a staff] was placed on the very highest point of this mountain.’ with no mention of a cairn.

Some visitors though that the cairn on the summit might originally have been the result of climbers following the tradition of leaving a stone on the summit, (although one thought that the top of Snowdon had been lowered a bit by visitors taking the highest stones from the summit as souvenirs). No visitors described seeing what they thought was a prehistoric burial mound (a carnedd) on the summit. (See Snowdon archaeology)

Snowdon: ‘The Object [presumably a staff] was placed on the very highest point of this mountain’
Mudge, William (1762-1820), An account of the operations carried on for accomplishing a trigonometrical survey carried on by order of the Master-General of his majesty’s Ordnance in the years 1800, 1801, 1803, 1804, 1805, 1806, 1807, 1808 and 1809 by Lieutenant-Colonel William Mudge, RA, FRS and Captain Thomas Colby, R.E., Vol. 3 (London: printed by W. Bulmer and Co. for W. Faden, 1811), p. 77

1805 (21st July)
Here we observed a small pile of stones recently thrown up by some artillery-men employed by government;
Mavor, William Fordyce, (1758-1837) A tour in Wales, and through several counties of England: including both the universities ; performed in the summer of 1805, (London : 1806)
Also in:Phillips, Richard, Sir, A Collection of Modern and Contemporary Voyages and Travels, Volume 1, (1810), pp. 95-105

Manuscript in ink and watercolour, comprising 20 pages of sketches, together with a plan and geometrical view of  Snowdon, North Wales. Drawn by R.K. Dawson under the direction of his father Robert Dawson, instructor in surveying and drawing for the Corps of Royal Military Engineers.
The drawings were made in association with the work of Robert Dawson senior in surveying the country round Snowdon for the first edition one inch to a mile Ordnance Survey map of England and Wales.
This manuscript volume consists of drawings, with little text (the essays being illustrations), illustrating different methods and shadings to represent various topographical features such a bogs, estuaries, cliffs and mountains.
The subjects include:
First: Ground must be conceived as seen from above, by a vertical and single view
Second: Mountains, Hills and Hollows must be conceived as features varying the general face of the ground …
Essays in Shading and breaking level surfaces
Essays in shading and breaking Declivities
Precipice of Columnar Rocks such as occurs in N. Wales
Gradated Declivity such as occurs in the Eglwyseg cliff near Llangollen, Wales
Basaltic Rocks as they occur at the Giants Causeway
Assemblage of Declivities
Mathematical Forms applicable to Hills (5 figs)
Group of Hills
Chain of Hills
Plan and Geometrical View of the Mountain of Snowdon in N. Wales scale 1,000 ft = 2 ins showing Llyn Cwellyn, Dolbardarn Castle, Llanberis Lake, Llanberis, Llyn Gwinedd, Llyn y Ddinas, Beddgelert and Snowdon.
Essays towards the expression of ground in topographical plans. By Robt K. Dawson, Candidate for the Corps of Rl Engineers. Lichfield: 1815-1816, British Library, Cartographic Items, Maps C.21.e.7. 28 x 47 cm., ff. 21


Clarkes’ Principal Triangulation of Britain, 1860 showing how in 1825-1826, observations were made from Slieve Donard (Ireland) to Scar Fell (111 miles) and Snowdon (108 miles). The distance between Snowdon and Scar Fell was later calculated to be 102 miles, making it one of the biggest triangles in the whole survey.

A newspaper report firmly dates the erection of a cairn on the summit of Snowdon to September 1826, but other sources date it to 1827, possibly because it was constructed after the end of the tourist season (and was not reported until the following year), or it was further enlarged in 1827. This cairn was almost certainly constructed for the Ordnance Survey. They had completed their original survey of the area by 1820, and carried out a re-survey in 1842, and did not need to use Snowdon for local surveys between those dates, but they began their survey of Ireland in 1825 and there is firm evidence that they linked the surveys of Britain and Ireland together by triangulating mountain-tops in Ireland with Snowdon and other peaks in Wales and the west of England.

The cairn was described as having a staff in it, between 14 and 27 feet high on which people carved their names. The staff appears in three early drawings of the cairn (one of 1828 by John Orlando Parry, the other two undated) but not in the earliest photographs of the cairn taken in the 1860s.

In about 1828 the Rev. John Parker described the staff in more detail: ‘four thick and long planks, nailed all together, and placed on a large mound of stonework, by order of the Government in 1827.’ He explained that before it was put up, people had tried to take away the highest rock on the summit, so the height diminished.

The mound would have required a considerable quantity of stone, which was presumably gathered from the surrounding area, including any stones used in a boundary wall (if there had been one) and from the circular stone wall on the summit.

In 1841 military engineers were on the summit enlarging the 1827 cairn. Between 16th July and 21st November, 1842 Ordnance Surveyors took triangulation measurements from Snowdon to 28 different trig points in England, Wales and Ireland. Several visitors found the surveyor’s tents at the summit, but when the Bishop of Norwich visited his son who was one of the surveying Officers, in October 1842, in freezing conditions, he stayed in a wooden hut. His long letter to his wife, describing the excellent food he was served and the stormy night he spent on the summit in freezing conditions, is transcribed in full below.

At 3.30 p.m. on the 31st December 1845, Captain Drummond’s lime light at the top of Slieve Donard in Ireland was seen across the Irish Channel by an observer at the top of Snowdon, a distance of 108 miles.

The Ordnance Survey were back on Snowdon in 1886 and 1887 when surveying each county for the first edition of the 6 inches to the mile maps. Reports of their surveys in 1886, suggest that the base line of 6.93 miles on Salisbury Plain was checked against a base line established on the shores of Lough Foyle in Ireland in 1827-1828, via a series of triangles, including observations from Snowdon.

The re-triangulation of Britain from 1936 used Carnedd Ugain, about 850 metres (880 yards) to the north of the summit and only 25.6 metres (84 feet lower) than the peak of Snowdon because the summit was so popular with visitors. The surveyors spent 12 nights taking readings from Carnedd Ugain in August, 1937.

1803   William Mudge (1762-1820) reported on the triangulation of Britain for the Ordnance Survey
1816   Detailed survey and map preparation began in Caernarvonshire
1825   Captain Drummond invented the heliostat and lime lights for viewing distant trig points. They were later used on Snowdon
1826   A stone cairn was erected on the summit of Snowdon with a staff of planks set vertically above it, between 14 and 27 feet high
1826   Snowdon was one of the trig points surveyed from Ireland
1827   Edwin Toby Caulfeild described the cairn and staff on the summit
1828   Five visitors described the cairn and one, John Orlando Parry, sketched it and the little hut near-by
1829   Harry Longueville Jones, an archaeologist, confirmed that the cairn had been set up for surveying
1831   Hannah Williams also thought the cairn was for surveying
1832   Thomas Letts thought the cairn had been raised by contributions from climbers
1833   Samuel Lewis described the cairn and staff in his Topographical Dictionary
1835   Thomas Pryer reported that like others, he scratched his name on one of the stones in the cairn
1837   Elizabeth Bower’s conceited husband was determined to be higher than her by climbing the staff
1837   Thomas Turner made no mention of the cairn or staff
1839   The Rev, William Bingley confirmed that the staff was still in the cairn
1840   Two more visitors described the cairn and staff. One thought it had been set up at the suggestion of George IV
1841   In May, a local newspaper reported that sappers and engineers were building a column on the summit
1841   A visitor to Scarfell in the Lake district, the highest point in England, reported that surveyors had viewed a helioscope on Snowdon from it
1842   The Government published a list of many trig points, suggesting that Snowdon was established in 1842
1842   Hannah Wood found tents on the summit occupied by the surveyors
1842   The local newspaper suggested that the tents would serve as shelter for tourists
1842   Edward Stanley, Bishop of Norwich visited his son, one of the surveyors, on the summit in October
1842   Edward Stanley, Bishop of Norwich sent his son’s letter to Michael Faraday describing the ‘electrical suffusion’ he observed on the summit
1842   The German, Johan Georg Kohl described the tents on the summit
1842   (probably) A heliostat on Berule on the Isle of Man was seen from Snowdon
1845   A lime light on Slieve Donard in Ireland was seen by an observer on Snowdon
1855   Archaeologists thought that a beacon (for signalling threats of attack in Elizabethan or Georgian times) had been destroyed by the cairn
1886   The Ordnance Survey were back on Snowdon surveying for the new 6 inch to the mile maps
1886   A sketch in one of the Snowdon visitors’s books shows a flag on the top of the cairn
1887   Some of the Ordnance Survey team climbed Snowdon at night
1936   A trig point on Garnedd Ugain replaced the one on Snowdon for the resurvey of Britain

Equipment was brought to Rhuddlan in September 1802 …
Particulars relative to the measurement of a new Base Line on Rhuddlan Marsh in the year 1806.
Snowdon: ‘The Object [presumably a staff] was placed on the very highest point of this mountain’

Mudge, William (1762-1820), An account of the operations carried on for accomplishing a trigonometrical survey carried on by order of the Master-General of his majesty’s Ordnance in the years 1800, 1801, 1803, 1804, 1805, 1806, 1807, 1808 and 1809 by Lieutenant-Colonel William Mudge, RA, FRS and Captain Thomas Colby, R.E., Vol. 3 (London: 1811), pp. 77, 82-85
All the papers in this series appear to have been first published annually in the ‘Philosophical Transactions of the Royal Society‘.

Map of part of Caernarvonshire, 2 inches = 1 mile.
British Library, OSD306 marked: ‘Part of Carnarvonshire taken in 1816, 17,18,19 and 20 by R Dawson’ It was published at a scale of 1 inch to the mile in 1840-1841 after a revision during 1836-1840.
Hewitt, Rachel, Map of a Nation, (2010), p. 191
Alfrey, Nichols, ‘Landscape and the Ordnance Survey 1795-1820’ in Alfrey and Daniels Mapping the Landscape, essays on art and cartography, (1990)

1825-1826 Beginning the Survey of Ireland
The pioneer [surveying] company … sailed for Ireland and landed at Belfast on the 15th July, 1825; where the survey was to commence and carried from north to South. … This arose from the greater facilities of connecting these by triangulation across the Irish channels, making the Isle of Man a stepping stone on the way.
[The invention by Capt. Drummond’s R.E. of a lime light (for making a distant trig point visible at night) and the heliostat which used a mirror to reflect the sun’s rays during the day, enabled the survey continued with] one of the largest heliostats, and the great theodolite, a gigantic triangle was accurately observed, which embraced the most conspicuous peaks in Ireland, England and Wales. The observatory was stationed at Slieve Donard, the highest of the Mourne Mountains in Ulster, rising to an altitude of 2788 feet, a few miles from the shore of Dundrum Bay. Looking in an easterly direction the mountains of Cumberland rose boldly from the mainland, towering above the intervening hills on the Isle of Man and culminating in Scar Fell, 3,230 feet above sea level. At this elevation, Lieut. Larcom R.E. was stationed in charge of the heliostat. Notwithstanding the advance season of 1826, when the hills were covered with snow, successful observations were taken, from which the computations determined the distance to be 111 miles. – the greatest angle measured on the O.S., Then the instrument was directed to Snowdon, rising to 3,590 feet. Here a heliostat observation made the distance 108 miles, and afterwards when the expedition returned to Great Britain, the third side of the Great Triangle [i.e. between Scar Fell and Snowdon] was ascertained to measure 102 miles
Article 7. The Ordnance Survey. The Westminster Review, vol. 117 (1882), pp. 512-513 (Review of various books on the history of the OS.)
Goode, Samuel, Mance’s Heliograph or Sun Telegraph, Journal of the Royal United Service Institution, Volume 19 (1875), p. 538

A newspaper report firmly dates the erection of the cairn on the summit to September 1826, but other sources date it to 1827, possibly because it was constructed after the end of the tourist season, or it was enlarged the following year.
The descriptions of this wonder of our land, are too familiar to afford the introduction of anything new on this otherwise inexhaustible topic; but government has within the last month, either with some view to ornament, or perhaps utility in rendering it a more conspicuous land-mark from St George’s and the Irish Channels, had a party of ten workmen engaged, during a week, on the summit (which is a flat surface of not more than 15 feet in diameter), in the erection of a pyramid of stones, surmounted by a stout high board, well coated with pitch and pointed at the top, adding in all about 25 feet to this prominent and highly picturesque elevation.
Sheffield Independent and Yorkshire and Derbyshire Post, 23.9.1826

An ancient monument destroyed in Ireland to make a trig point.
Colby, who supervised the survey of Ireland ordered the demolition of an ancient monument on Slieve Donard in 1826 to make the trigonometrical station there. Slieve Donard was one of the trig points in Ireland which was visible from Snowdon.
ANDREWS, J.H., A Paper Landscape, The Ordnance Survey in Nineteenth-Century Ireland. (1975), p. 163

The presence of the staff in the cairn was confirmed by a visitor in 1827 but it is unlikely that it was intended for the navigation of vessels because Snowdon is so often under cloud.
A staff is erected on the summit, inserted in a large conical heap of stones, by the order of the Government, as a mark for vessels in the Irish Sea. … The apex of Snowdon is about eighteen feet square
Caulfeild, Edwin Toby, A tour through part of North Wales, October 1827 [1827], pp. 6, 8 (note)

In 1828 an anonymous tourist pointed out how useless the staff would be:
the space on the summit only about 10 feet square is ?newly occupied by a wooden pillar 27 feet high erected by Government about 3 years since but with little utility as it cannot be seen one hour in fifty;
Anon, A journal, with sketches, of a walking tour from Kington to Aberystwyth and through parts of North Wales, 1828 and Manuscript Account of a Tour into Wales undertaken May 1828 [in north Wales], NLW MS 6716D

In the same year, Charles Clark described the cairn as a grotto, but whether it was hollow, or simply acted as a wind break is not clear:
on the top was a large grotto built with a thick mast of wood on top of it to shelter travellers from the cold piercing wind which we found very great;
Clark, Charles B., Tour of Wales in August and September, 1828, NLW MS 15002A

Also in the same year Prince Puckler-Muska, implied that it was just:
A pile of stones, in the centre of which is a wooden pillar, marks the highest point. … I scratched my name near a thousand others on a block of stone,
Prince Puckler-Muska, Tour in England, Ireland, and France, in the years 1828 & 1829: with remarks on the Manners and Customs of the Inhabitants, and Anecdotes of Distinguished Public Characters by a German Prince, London: 1832. (2 vols.), p. 295; Philadelphia 1833 (4 vols.)

Yet another visitor in 1828, the Welsh harper John Orlando Parry, (1810-1879), sketched the hut and the cairn which appears to have an entrance into the base of it, or at least a concavity on the surface. See summit huts
Sketch of ‘The highest Peak of Snowdon’ showing a pillar on top of a beehive shaped mound of stones and an igloo shaped hut below it, both big enough for travellers to shelter in.
On the highest summit is a Pillar (no. 1 in illustration) and a little lower down – a little stone hut for travellers- to shelter in (no. 2 in illustration) … Well it was no use staying there as we were so wet and so hot! – so we sallied out of this little hut …
Parry, John Orlando, (1810-1879), ‘A Journal of a tour in the Northern part of Wales, made in September 1828’, NLW minor deposits 293B

John Parker described the staff in more detail: ‘four thick and long planks, nailed all together, and placed on a large mound of stonework, by order of the Government in 1827.’
He continued:
‘I am rather annoyed by this heap of stonework, and these planks above it, that prevent our turning around in the same place to see the whole panorama.’
{Before it was put up, people tried to take away the highest rock on the summit, so the height diminished. The workmen who put up the mound of stone, slept in the little stone hut} ‘for a fortnight, in the fine summer weather in 1827.’
Parker, John, (1798-1860), The Passengers (Travels through Wales), (London, 1831), pp. 160, 179-180, 191

The union of all these ridges, forms a vast solid mountain, terminating in a sharp peak, rendered still more acute by the erection of a cairn of stones, and a high signal post, constructed by the officers of the late ordnance surveying expedition.
Jones, Harry Longueville, Illustrations of the Natural Scenery of the Snowdonian Mountains Accompanied by a Description Topograhical and Historical of the County of Caernarvon (London 1829), p. 18

[The summit] rises almost to a point on which is placed a conical heap of stones and upon these a lofty pillar of wood erected by the engineers when they were making the trigonometrical survey.
Williams, Hannah, Journey through Shropshire, Wales, Ireland & Lancashire, 1831, Worcestershire Record Office, 899:866/9522

we gained the wall of stones (raised by the accustomed tribute of a single one, from each visitor) at the very pinnacle of the mountain, … What could we see? A stone wall and three gloomy countenances; not only our account of the shelter afforded by the wall but because its attainment seemed like some great feet to boast of.
Letts, Thomas 1832 NLW MS 21690B ‘1832 August Manchester, Liverpool, By coach to North Wales with Mr Tho[Thomas] Boyce. Joined by Messrs [John] Russell and Badderly.’

The highest summit of Snowdon is called Y Wyddfa or “the conspicuous” and rises almost to a point affording space only for a small enclosure of loose stones, where the traveller may take refreshment, while resting from the toil of his arduous ascent, and within which a pole, consisting of four thick planks inserted in a mound of stone, was erected by order of government in 1827.
Lewis, Samuel, A Topographical Dictionary of Wales, (1833), vol. 2, Llanberis
[The same text about the summit is in 1840 and 1845 editions, but details of hotels etc. were changed.]

In the centre of the summit is a high pile of stones, serving as the rude pedestal of a wooden pillar which was erected here by the officers of the Ordnance surveying expedition. Before descending I mounted the pile and cut my initials on the pillar.
Pryer, Thomas, ‘A Journey through North Wales in the month of August 1835 by Thos. Pryer’, illustrated with engraved prints by Gastineau and a few others. NLW MS 3138C

I contented myself by sitting down on a heap of stones on the summit & admiring the vastness of the landscape around me but Henry, more adventurous, must needs mount on a wooden pillar raised above the stones, & was insufferably conceited at having thus occupied a more elevated position than myself
Bower, Elizabeth, (with her ‘newly acquired husband’) Dorset Record Office, D/BOW:kw 209 / D.I/KW209, pp. 125-126

we were glad to shelter ourselves under a dwarf wall which has been erected for the comfort of tourists, and to discuss some brandy and biscuits. We now stood on the highest pinnacle of the mountain upon a space not more than 20 feet in diameter.
Turner, Thomas, (of Gloucester) Narrative of a Journey associated with a Fly, from Gloucester to Aberystwith and from Aberystwith through North Wales, July 31st to September 8th 1837, (London, 1840), pp. 116- 11

On the summit is piled a heap of stones to which is fixed, perpendicularly, a plank of wood about fourteen feet in height.
Bingley, W., Rev, Excursions in North Wales including Aberystwith and the Devil’s Bridge, intended as a guide to Tourists by the late Rev W Bingley. Third edition with corrections and additions made during Excursions in the year 1838 by his son W.R. Bingley B.A. of Trinity College, Oxford, with a … map by J. and C. Walker. (London, 1839), p. 126

A Great pole was now on the summit set up by order of the Government
Black’s Guide, p. 102

On top is erected a little circular tower of stone and on this a beacon constructed of several planks on beams as a landmark
Napier, C.E., Diary of Captain Charles Elers Napier (step son of Admiral Sir Charles (born 22.5.1812)), of a walking and fishing tour in Wales, Scotland and Ireland, National Maritime Museum, Greenwich, JOD/80, [p. 16]

Two planks, 20 ft long, set upright in a heap of stones to make the summit visible from a distance (a suggestion of George IV in 1821).
Maymott, William, ‘William Maymott, July and August, 1840, Tour in north Wales’, Cardiff Central Library, MS 2.848

The 1841 cairn
We understand that Lt. Craig of the Military Engineers, is sojourning at the Victoria Hotel having under his command a party of sappers and engineers creating a column on the top of Snowdon.
Caernarfon and Denbigh Herald, 22.5.1841

It was a perfect pyramid of broken rocks intermingled with turf, and terminating in a heap of large stones.
S.S., Bangor to Llangollen, English Journal, vol. 1, (1841), pp. 21-22

[In 1841] I joined a reading party in Keswick. On an excursion to Scarfell I found a small encampment of ordnance surveyors with theodolite and heliostat to observe the bearing of Snowdon. A corresponding station was set up on the top of Snowdon, whence, after many days’ waiting the light reflected from the sun by the mirror on Snowdon became faintly, but clearly visible 
Memories of My Life by Francis Galton, (1908), pp. 59-61

A list of all the Principal triangulation points, some of which date back to 1792. It includes places in England, Scotland, Wales and Ireland.
Slieve Snaght, first used 1827
Snowdon, first used 1842
The station on this celebrated mountain in north Wales is upon the highest peak, and is marked by a pile 20 feet in diameter, beneath which a hole is bored in the rock to denote the centre.
Clarke, A.R., Captain, Ordnance Trigonometrical Survey of Great Britain and Ireland, Account of the observations and calculations, of the principal triangulation: (London: 1858), pp. 36, 153

arrived at the summit of Snowdon having ascended 3572 feet in [blank] hours. Found tents erected for sappers & miner for observations & several parties.
Hannah Wood, Book of Sketches, National Library of Wales, DV26 (PD281)

The corps of engineers have sent down a company of sappers and miners to make preparations for the arrival of some efficient officers to complete or repeat a trigonometrical survey of these hills and the surrounding country; and the circumstance is fortunate for the tourist, as their tents will afford him shelter from the gust.
Carnarvon and Denbigh Herald and North and South Wales Independent, 18th June 1842

Letter: Edward Stanley, Bishop of Norwich, to Michael Faraday, 2 November 1842
I enclose a letter from my son, Lieut. Charles Stanley, R.E., [died 1849 aged 30, see Gents. Magazine, vol. 33, p. 341] now encamped on the summit of Snowdon for the purpose of taking triangles for the new Ordnance Survey describing a fine case of electrical suffusion occurring on the evening of 20 October. … It appears to me that the observatory which is about 10 or 12 yards above the officers’ hut on the very pinnacle of the mountain must have received the discharge of an electric current,
Papers of Michael Faraday, Royal Institution of Great Britain, ms. F1 K30;
Faraday, Michael, Correspondence of Michael Faraday (ed. Frank A J L James), vol. 3, 1841-1848, (1996), pp. 104-105, Letter 1443

Camp Snowdon, Monday Oct. 20, 1842
—- Left Chester at 7 o’clock [and] found myself on my way up Snowdon soon after 12. The morning was perfect …
There was Snowdon’s peaks before me white and sharp as Alps in their new clad ermine garment of Snow … The peak … appeared again and the camp became visible like small dim excrescences on an inclined plain of snow – soon after this, three figures were visible with a black speck moving rapidly to and fro ????? ????? & soon one of the little figures shot ahead from the nest? followed by the black speck – it was not necessary to use my Telescope to ascertain that the figure was dear Charles & the speck his black dog, ???????? he bounded & soon we met and he did look so happy – the two others joined us soon Mr Pipon and Hankesson … within a few paces of the top one of the men came on to say that the long sort for, and in vain looked for the Heliostat of Axe Edge was visible and up ran Pipon and Charles to the observatory to verify the result and note down the angles – leaving me to the care of James to do the honours of his house [on the summit] …  I still reluctantly retired to ‘visit’ the Observatory & had the extreme pleasure of being present when not only Axe Edge but two others, Whittle Hill & Bollings [Billinge] 88 & 65 miles, were again visible & noted down. …
Ever yours
E Norwich
Letter from Edward Stanley, (1779–1849) Bishop of Norwich (1837 -1849), Cheshire Archives and Local Studies, Stanley of Alderley Records, DSA/201,

Upon the extreme summit is a huge wooden pillar placed on a large mound of stonework, erected by the government in 1827, covered with hosts of names of persons who this aspire to immortalise themselves …
Parry, Edward, 1798-1854, Cambrian Mirror, or a New Tourist Companion through north Wales (1843).  p. 101
Anon, The stranger’s best guide to Bangor, Penrhyn Castle and the slate quarries, and through the most picturesque scenery of Carnarfonshire with directions how to proceed at the least possible expense and loss of time. (Bangor, printed by Catherall, Bangor and Chester [1856]), p. 62 [and subsequent publications]

The mountain tapered at last into a complete cone, terminating in a summit, on which there was just room enough to spread out a tent for the protection of some mathematical instruments. The soldiers in charge of this tent, erected with a view to a new survey of the country, had constructed a small path of stones around their canvass mansion, and thus it became easy to enjoy the prospect on every side. The officer of engineers in command of the post had pitched several tents, a little lower down, for the accommodation of himself and his men.
Snowdon lies right in the centre of the British World, and commands from it summit, views at once of England, Scotland, Ireland, and Wales and of Anglesey and Man. The atmosphere around these English [sic] mountains, to be sure, is seldom clear enough to allow one the full enjoyment of the whole horizon. The officer told me that during the two months he had spent on Snowdon, he had not seen the coast of Ireland more than four times, and yet the summer … had been a remarkably beautiful one.  {Comments on the good weather during the trip}
Kohl, Johan Georg, Reisen in England und Wales, (Dresden, 1844)
Kohl, Johan Georg, England, Wales and Scotland, (London 1844)  (Abridged translation by Thomas Roscoe)
Kohl, Johan Georg, Travels in England and Wales [1845] (Translated into English by Thomas Roscoe), Reprinted (London 1968), pp. 68-69

Drummond Light
On the 31st December, 1845, Drummond’s Lime light was seen across the Irish Channel at 3.30 p.m. from the top of Slieve Donard in Ireland by an observer at the top of Snowdon, a distance of 108 miles.
Knight, Charles, The English Cyclopaedia, vol. 3, (1867), p. 683
[It is possible that this took place in 1842 rather than 1845]

Using a heliostat, Berule on Isle of Man was seen from Snowdon
Cadastral Survey [25 inches to the mile] of Great Britain, The Edinburgh Review, Or Critical Journal, Volume 118, (1863), p. 386

Beacon station, on the summit of Snowdon, now obliterated by the heap of stones raised by the Ordnance Surveyors.
Anon, List of Early British Remains in Wales, no 5 Caernarvonshire south, Tumuli or Carneddau or Beddau, Archaeologia Cambrensis, 1855, p. 177

The Ordnance Survey returned to prepare for the new 6 inch maps of Britain. The drawings and photographs of the cairn show that it was not enlarged for this purpose.
The summit of Snowdon is now being used as an observing station by the Ordnance Survey authorities, who are at present engaged in, making a trigonometrical survey of the neighbouring mountains and district in Carnarvon, for the purpose of laying down the basework previous to the detail survey being made for the new ordnance maps of the county. An observatory is temporarily erected on a large stone pile which crowns the top of the mountain, from which observations are taken to all principal points in sight, in order to obtain the altitudes, and horizontal distances between each of the same, the chief instrument used for this purpose being a 12-inch theodolite, of one of the latest patterns. These operations will probably occupy a few weeks, owing to this lofty eminence being a great portion of the time in clouds of mist, but during the last few days some very clear weather has been experienced, which has facilitated the work, and enabled many who have lately made the ascent in the early mornings to witness some very fine sun rises and excellent views. Lines of sight are obtained and measured from the observatory in Holyhead Mountain, Carnedd Dafydd, Plinlimmon, Cader Idris, Moelygest, and many other distant points, by means of a triangulation brought through the country from Salisbury Plain, where a base of 6.93 miles was laid and measured with Colby’s compensation bars in 1849, and checked by a base line measured on the shores of Lough Foyle in Ireland in 1827-8, connected to the former by a series of triangles. The accuracy of all these operations will be seen by the fact that the difference of the length of the base line on Salisbury Plain, as actually measured and calculated from the Lough Foyle base was only 4.7 inches. The operations in the county of Carnarvon are being rapidly pushed forward, when, upon its completion, maps of great accuracy will be published on scales of ten feet to the mile for towns of over 4000 inhabitants, 25 inches to the mile for parish maps, and six inches to a mile for the county maps, being the same scales as the remaining counties of Wales are published on, together with the greater number of the English counties. Snowdon was also used in the old survey, the centre mark on its summit being again utilised, and for a check, on the new work round it. It may be mentioned that the survey for the old maps of one inch to the mile was first commenced in 1791, but upon a recommendation of a committee in 1854-5 the scales were increased to the sizes now used, for many purposes, and as every little detail will be shown in them, their superiority will be recognised and their usefulness proved to many.
The North Wales Express, 24th September 1886
Summary in The Western Mail, 24th September 1886
Preston Herald – Saturday 25 September 1886
North Wales Chronicle – Saturday 09 October 1886
Summary in Edinburgh Evening News – Monday 11 October 1886
Hampshire Advertiser – Saturday 25 September 1886 – From Liverpool Courier

A rather poor sketch of the summit, showing the two huts with the cairn between them, has a flag on a pole on the top of the cairn.
Visitors’ book, NLW MS 16085C, f. 11r

1887, 6th August
Some of the Ordnance Survey officers left a note in the Snowdon Visitors’ book.
Joseph B Duro, Ordnance Survey, Pen Pass, Llanberis
G F Murphy, O.S., Pen y Pass
Party started from Pen y Pass 11.30 pm. 6.8.87, arrive 2 am 7 Aug, 87 deuced wet awoke host & had ????? 1s a bottle to save being drown [page trimmed]
William Parton Ordnance Survey camp
John Young O.S.
Thomas Shaw
Corporal Hughes R.E. 13 Berry Street, Conway [with other members of the Hughes family from the same address.]
Joseph B Duro O.S. camp Pen Pass, Llanberis, started up Snowdon Saturday night August 7th 1887 at 11 p.m. and arrived on the summit at ½ past 1, wringing wet through on Sunday morning Returned daylight. W Parton accompanied the same party in awful rough weather hoping sometime to meet again.
R Lloyd Jones [and two others] Ordnance Survey camp Pen-y-pass, Llanberis
Snowdon Visitors’ book, NLW MS 16085C, f. 127r

A Trig point on Garnedd Ugain replaced the one on Snowdon in 1936.
Surveying first took place 27-28.6.1937. They tried surveying 8 stations from 11 Aug. and it took 12 nights to get all the sightings they needed.
Davies, John, Primary Trigs in Wales (2012), pp. 196, 130

Much has been written on the Ordnance survey of Britain, including:
Harley, J. B. and Oliver, R.R., Introductory Essay, The Old Series Ordnance Survey Maps of England and Wales. Scale: 1 inch to one mile. Vol. 6, Wales, pp. vii-xxv