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Description of Harbour Screw-Cramps, for temporary use in 
binding together the Stones in the Construction of Harbour 
or other Marine Works. By THOMAS STEVENSON, Esq., 
Civil Engineer, F.R.S.E., F.R.S.S.A. (With a Plate.) 
Communicated by the Royal Scottish Society of Arts.* 
Of all engineering operations, the construction of marine 
works in exposed situations may be regarded as the most 
precarious and difficult. The great force to which such 
erections are subjected, has recently been put to the test of 
direct experiment, by means of an instrument designed by 
me for the purpose, which has been named the Marine Dyna- 
mometer. The observations which were made with this in- 
strument I lately communicated to the Royal Society of 
Edinburgh, and as the facts which are there stated are inti- 
mately connected with the subject of the following observa- 
tions, I beg leave to give a brief digest from that Society’s 
Transactions. 
‘In the Atlantic Ocean, according to the observations 
made at the Skerryvore Rocks, the average result (of the 
force of the sea) for five of the summer months, during the 
years 1843 and 1844, is 611 lb. per square foot. The ave- 
rage results for six of the winter months, during the same 
years, is 2086 lb. per square foot, or ¢hrice as great as in the 
summer months. 
“The greatest result yet obtained at Skerryvore was 
during the heavy westerly gale of 29th March 1845, when a 
pressure of 6083 lb. per square foot was registered. The 
next highest is 5323 Ib. 
“In the German Ocean, according to the observations 
made at the Bell Rock, the greatest result yet obtained is 
3013 lb. per square foot. 
“ It thus appears, that the greatest effect of the sea which 
has been observed by the instrument, is that of the Atlantic 
at Skerryvore, which is nearly equal to three tons per square 
foot.’ t 
* Read before the Royal Scottish Society of Arts on 11th December 1848, 
f Trans. Roy, Soc, Edin., vol. xvi. 
