162 CAPTAIN A. E. CLAEKE ON THE COMPAEISON OE ENGLISH AND FOEEIGN 
as the units of measure in the triangulation of the several countries, it would be 
impossible accurately to express the length of the arc of parallel in terms of any one of 
the standards. 
It was therefore necessary that a comparison of the standards of length should be 
made; and as we had a building and apparatus expressly erected for the purpose of 
comparing standards at this office, the English Government, on my recommendation, 
invited the Governments of the several countries named to send their standards here ; 
and we have had the following compared with the greatest accuracy : — 
1. Russian Standard double Toise, P. 
2. Prussian Standard Toise. 
3. Belgian Standard Toise. 
4. Platinum Metre of the Royal Society, compared with the Standard Metre of 
France by M. Arago. 
5. English Standard Yards, A, B, C, 29, 47, 51, 55, 58. 
6. Ordnance Survey 10-foot Standard Bar. 
7. Indian 10-foot Standard Bars, new and old. 
8. Australian 10-foot Standard Bars. 
9. In addition to the above, the 10-foot Standard Bar of the Cape of Good Hope was 
compared here in 1844. 
We have invited the Governments of Austria, Spain, and the United States of America, 
also to send their standards. We have been promised that of Austria, and but for the un- 
fortunate war in which she has been lately engaged, we should have received it before this. 
I have entrusted the execution of the work of comparison and the drawing up of the 
results to Captain Alexander R. Clarke, of the Royal Engineers, who designed the 
apparatus used. The numerous comparisons to be made entailed a great amount of 
labour upon him and his assistants, Quartermaster Steel and Corporal Compton, of the 
Royal Engineers. 
Before the connexion of the triangulations of the several countries into one great 
network of triangles extending across the entire breadth of Europe, and before the dis- 
covery of the electric telegraph and its extension from Valentia to the Ural Mountains, 
it was not possible to execute so vast an undertaking as that which is now in progress. 
It is, in fact, a work which could not possibly have been executed at any earlier period in 
the history of the world. The exact determination of the figure and dimensions of the 
earth has been the great aim of astronomers for upwards of two thousand years ; and it 
is fortunate that we live in a time when men are so enlightened as to combine their 
labours to effect an object desired by all, and at the first moment when it was possible 
to execute it. 
A full detailed account of the ‘ Comparisons of the Standards of Length,’ with 
numerous plates, has just been published, and may be obtained from the agents for the 
sale of the publications of the Ordnance Survey. 
Ordnance Survey Office, 
Southampton , 14 th November, 1866. 
Henry James, Colonel B.E. 
