114 
(5) But while there is considerable preliminary evidence 
in favour of a variability in the heating power of the sun, 
and while this is constantly accumulating we must not deem 
it impossible that the sun affects ‘the earth in some other 
way. 
There is ground for supposing that the moon affects both 
the magnetism and meteorology of the earth in a way 
which we do not at present understand, and it is possible 
that the sun may have a similar influence. 
Since writing the above I have leaimed that Mr. Baxen- 
dell made use of the method of mean departures described 
in this communication in one of a remarkable series of 
papers which he presented to this Society on March 8th, 
1864. But I have no reason for supposing that he was 
aware of the peculiar characteristics of the method devised 
by Mr. Dodgson and myself in virtue of which we can with 
comparatively little trouble ascertain the exact periods of 
inequalities which are crowded very near together in the 
time-scale. 
On a form of representing the velocity at any point of 
an incompressible fluid under conservative forces,’’ by 
E. F. Gwyther, M.A. 
1. The velocity at any point of a fluid may be repre- 
sented in other forms than the usual velocity potential or 
the vector potential of Helmholtz. 
The form <r= v<^ corresponds to the case when SaSp is a 
complete differential without a factor ; let us imagine it to 
be made a complete difierential by a factor that is to be of 
the form 
0’ = Jc^\p 
or to be a combination of the two, thus — 
(T= V0 h 
2. First let us consider the circumstances accompanying 
the forms. If So-Sp is integrable by a factor the condition 
is ScrVo" = 0 or Scrp = 0. 
