43 
the air pumped off, for 24 hours. There was then no frost, 
but a bright column of mercury, which on erection remained 
suspended, the pump having been worked so as to remove 
the last trace of air. The tube was not left standing, but was 
inverted and erected for a few minutes each day for 8 da} T s, 
including this morning. When the pump was again worked, 
and the tube sealed by clips on the indiarubber before bring- 
ing it to the Society’s rooms — which somewhat difficult 
undertaking has been accomplished by Mr. Foster, who has 
assisted me throughout in these experiments. (On being 
erected in the Society’s rooms the mercury remained sus- 
pended for about 1 5 minutes; it then gave way with an audible 
click and sank to such a level as showed that there had not 
been air pressure of l-20tli of an inch on the lower end.) 
This experiment shows that the cohesion of water and 
mercury, and their adhesion to each other and glass, will 
withstand a tension of 3 atmospheres or 90 inches of mer- 
cury, being one atmosphere more than was shown by the 
former tube. 
But as I have been of opinion from the first that the limit 
of cohesion, whatever may be that of adhesion, is a much 
greater quantity, my object in making and recounting these 
experiments has not been so much to prove a somewhat 
higher cohesion as to throw light upon the circumstances 
on which the successful suspension depends. 
The fact that the frost on the glass, the imperfect draining 
up of the water, and the nonsuspension of the mercury all 
occur together, and may all be removed by time or by the 
complete removal of the air from the glass, seems to show 
that even when glass is completely wet or covered with 
water there may be and generally is a considerable quantity 
of air still adhering to the glass. 
As regards the limit of the cohesive or adhesive strength 
of water and mercury, I conceive this to be beyond any test 
that can be applied by gravity. Several feet more might be 
