213 
of Edinburgh^ Session 1863-64. 
in a species of constraint— that on the discharge of this force the 
muscular fibril contracts, and that the constraining force is immedi- 
ately renewed. It has been supposed that the force here operative 
is heat, j^et electricity seems better fitted for the purpose. In 
support of this view is cited the analogy, indicated by some autho- 
rities, between the structure of the muscular sj^stem and that of the 
electric organs in the gymnotus and torpedo. 
If such a view, under whatever modification, be rejected, heat must 
be resorted to as the source of animal power. 
To prove heat to he the source of animal power, it must be shown 
that the products of eremacausis, under forcible muscular exertion, 
both account for the whole temperature manifested in the mean- 
time, and leave a surplus sufficient to be metamorphosed into the 
calculated equivalent of the mechanical effect produced by the 
entire amount of that exertion. 
Chemists pronounce that the amount of heat in the combustion 
of hydrogen and carbon, whether slow or rapid, is exactly propor- 
tioned to the products in water and carbonic acid ; nevertheless, it 
may he doubted if two circumstances have been taken into account 
in their estimate as respects the living body, viz., the disturbance 
of electric equilibrium in such combustion, and the reciprocal con- 
vertibility of heat and electricity, so that it may turn out that, with 
the same amount of material products, there may he room for a 
reciprocal variation in the proportions of these forces developed, 
Whence, though the product in carbonic acid and water be in 
exact proportion to a given exertion of animal power, the question 
appears to be still unsolved. Whether heat, or electricity, or both 
jointly, represent the equivalent of mechanical force put forth in 
such exertions. 
2. On Sun Spots, and their connection with Planetary Con- 
figurations. By Balfour Stewart, Esq. Communicated by 
Professor Tait. 
The author was led to examine the sun pictures taken by the 
Kew Photoheliograph, with the view of ascertaining if any con- 
nection exists between the behaviour of sun spots and planetary 
configurations. 
