174 
making mercury adhere to the tubes by wetting them with 
sulphuric acid or water. Not being able to use mercury 
the tensions which he obtained were comparatively small, 
and although he seems to have considered that greater 
tensions might be obtained he mentions one or two atmo- 
spheres as probably possible. It would therefore appear 
that he had not conceived the possibility of the cohesion of 
liquids being comparable with that of solids. 
M. Donny appears to have been influenced in adopting 
this limit to his idea of cohesion by a passage from Laplace, 
Mecanique Celeste , Supplement au X e livre, p. 3, which he 
quotes. 
Laplace, who was the first to investigate systematically 
the phenomena of capillary attraction, proceeded on the 
hypothesis that the molecules of a liquid exercise attraction 
for each other at insensible distances only, and from this 
assumed attraction he deduces the surface phenomena. The 
entire passage quoted by M. Donny is too long to intro- 
duce here, but the gist of it is comprised in the following 
extract : — 
66 Son expression analitique est composite de deux termes: 
le premier, beaucoup plus grand que le second , exprime 
V action de la masse terming par une surface plane ; et je 
pense que de ce terme dependent la suspension du mercure 
dans un tube de barometre a une hauteur deux ou trois 
fois plus grande que celle qui est due a lapression de V atmo- 
sphere, le pouvoir ref ring ent de corps diaphanes, la cohe- 
sion, et generalement les affnites chimiques” 
Laplace here speaks of the suspension of mercury to 60 
or 90 inches as if it were a well known phenomenon ; but 
I cannot find any reference to experiments, or indeed any 
further mention of the phenomenon, in his memoir. 
I did not refer to Laplace in the first instance, although 
I knew well that it is to him we are indebted for the theory 
of surface tension almost in the form now accepted, because 
I wished to avoid all reference to molecular hypothesis, and 
particularly the molecular attractions assumed by Laplace, 
