96 
Next, taking the general case of such filaments, we have 
always 
1 + &0. +^Tp.e = 0 
which shows that the vector D^. v (pi + &c. is proportional 
to Tp directly and to the radius of curvature of the filament 
inversely. 
The only equation which we are able to obtain from this 
form of equation follo ws from Sep = 0 
whence = 0. 
From the equation Vpvp 2 = 0, we can not draw any con- 
clusion as we have no convenient expression for vp 2 . 
Turning to the terms which the elasticity of a viscous fluid 
introduces, namely, ^vDJogH. and noticing that by the 
equation of continuity d = H</>, where D$ = 0, we see that the 
elasticity will generally give rise to vortex motion in a vis- 
cous fluid ; and that the condition that it may not do so is 
that H<£ may be some function of D^logH. 
“ A Sulphuretted Hydrogen Apparatus,” by Peter Hart, 
Esq. 
When hydric sulphide is only occasionally required, and 
then in small quantities, an apparatus which so furnishes it 
is useful, especially when it can be used repeatedly without 
washing out or replenishing. The one I have contrived 
seems to me to fulfil these conditions. There have been 
many invented, but they mostly require either many joints 
or especially formed pieces of glass. This one can be made 
by any one possessing only very small skill in fitting up 
apparatus. It consists of two test tubes, the larger of one 
inch internal diameter, the other of such smaller diameter 
as to slide easily without friction into the larger. This 
