52 PROCEEDINGS OF SOCIETIES. 
and also to give the elements for a correction to be made upon the 
quantity of water drawn off. 
Stops and guides, not shown in the sketch, serve to keep the 
floating cylinder off the sides of the vessel, and prevent it falling 
too far upon the rupture of the fibre. 
AIC AA 
ial 
The principle upon which the apparatus works is so simple that 
it hardly requires explanation. At the beginning of the operation 
the weight of the tube is wholly supported by the water ; by draw- 
ing off the water the support is very gently removed and the weight 
thrown upon the fibre. The relation between the actual weight 
put upon the fibre and the weight of water drawn off will vary 
for every different dimension of the containing vessel and floating 
cylinder, but in regularly shaped vessels it will always be in the 
direct ratio of the sectional areas of the floating vessel, and the 
difference between this and the sectional area of the containing 
vessel, z. e. in cylindrical vessels the sectional area of the ring of 
water surrounding the floating cylinder. 
In the apparatus brought down for illustration and actually in 
