190 Dr. P. EH. Chase on some Principles 
of solution, he decides that it is hopeless, and that we must 
give up trying to establish a relation between these quantities. 
Chemical action, he concludes, only disturbs the effect by 
altering the surfaces, and by developing parasitic heats. They 
may mask, but they do not produce, the true Bouty pheno- 
menon, which he believes is probably physical. 
The difficulties of making these measurements are exceed- 
ingly great; and, notwithstanding the ingenuity and skill dis- 
played, it seems to me possible that some error or unexpected 
source of disturbance may have modified the results. So far 
as | know, they have not yet been repeated; and I can hardly 
regard the experimental method used as perfectly safe*. 
[To be continued. ] 
XXI. Some Principles and Results of Harmonie Motion. 
By Pury Hare Cuase, LL.D. 
AWoEN two bodies, in relative motion, come into con- 
tact, pressure begins to act between them to prevent 
any parts of them from jointly occupying the same space. .... 
Any force in a constant direction acting in any circumstances, 
for any time great or small, may be reckoned on the same 
principle ; so that what we may call its whole amount during 
any time, or its ‘ ¢ime-integral,’ will measure, or be measured 
by, the whole momentum which it generates in the time in 
question?’ (Thomson and Tait, ‘ Natural Philosophy,’ i. sec- 
tions 294, 297). 
No relative motions can be more important, and no contact 
more complete, than those which exist between the all- 
pervading luminiferous zether and the sun. In the conversion 
of tangential luminous waves into spherical vibrations, gravity 
is acting In a constant direction towards the sun’s centre. 
The amount of its activity upon each ethereal particle, y, or 
its time-integral during each cyclical period, ¢, is measured 
_ * T find that a method exactly like that used by Bouty was suggested 
by Clerk Maxwell, ‘ Elementary Electricity,’ p. 146. 
+ From the Journal of the Franklin Institute, January 1885. Com- 
municated by the Author. 
This paper has been written, in part, to meet a desire which has been 
expressed by some members of the Royal Astronomical Society for an 
introduction to the article on “Harmonic Motion in Stellar Systems” 
(Phil. Mag. Sept. 1884). The author will feel under obligation to any 
meade who will inform him of other points which need further eluci- 
ation, 
