* 
252 On the Transverse Strain, 
been made on it by different philosophers, 
from Mariotte down to our own times, and 
they have generally agreed, when properly 
conducted, in giving moderate extensions 
proportional to the extending forces, we can 
scarcely doubt that it is a law of cohesion. 
An experiment or two by Dr. Robison it 
may not be useless to quote, He says, “* We 
made experiments on fine slips of gum caout- 
chouk, and on the juice of the berries of the 
white bryony, of which a single grain will 
draw to a thread of two feet long, and again 
return to a perfectly round sphere. We 
measured the diameter of the thread by a 
microscope, with a micrometer, and thus 
could tell in every state of extension the pro- 
portional number of fibres in the sections. 
We found that though the whole range in 
which the distance of the particles was 
changed (varied) in the proportion of 13 to 
1, the extensions did not sensibly deviate 
from the proportion of the forces.” 
“The same thing was observed in the 
caoutchouk, as long as it perfectly recovered 
its first dimensions. And it is,’ continues 
the Doctor, ‘ on the authority of these ex- 
periments that we Teche to announce this 
as a law of nature.” 
