613 
of Edinburyh, Session 1881-82. 
liquid mass in two equal or unequal portions, so far asunder 
tliat each is approximately spherical, but disturbed to slightly 
prolate figures (according to the welbknown investigation of 
equilibrium tides, given in Thomson & Tait’s Natural Philosophy, 
§ 804), and to the more prolate figures which would result from 
subtraction of energy without change of moment of momentum, 
carried so far that the prolate figures, now not even approximately 
elliptic, cease to be stable, is peculiarly interesting. We have a 
most interesting gap between the unstable Jacobian ellipsoid 
when too slender for stability, and the case of smallest moment 
of momentum consistent with stability in two equal detached 
portions. The consideration of how to fill up this gap with 
intermediate figures is a most attractive question, towards 
answering which I at present can offer no contribution. 
(j) When the energy with given moment of momentum is either 
a minimum or a maximum, the kinetic equilibrium is clearly stable, 
if the liquid is perfectly inviscid. It seems probable that it is 
essentially unstable when the energy is a minimax • but I do not 
know that this proposition has been ever proved. 
(h) If there be any viscosity, however slight, in the liquid, or 
if there be any imperfectly elastic solid, however small, floating 
on it or sunk within it, the equilibrium in any case of energy 
either a minimax or a maximum cannot be secularly stable ; 
and the only secularly stable configurations are those in which 
the energy is a minimum with given moment of momentum. 
It is not known for certain whether with given moment of 
momentum there can be more than one secularly stable configur- 
ation of equilibrium of a viscous fluid, in one continuous mass, 
but it seems to me probable that there is only one. 
2. Notes on Atmospheric Electricity. By C. Michie Smith. 
Before leaving for India, in the end of 1876, it occurred to me 
that, as almost nothing seemed to be known about atmospheric 
electricity in the tropics, it would be well if I could take with me 
the apparatus necessary for making observations on it. I ac- 
cordingly communicated with Sir William Thomson, who kindly 
obtained for me a grant from the British Association, for a 
