1885.] 
133 
The Heat of the Sun. 
enlirdy endorsing Prof. Young's words, there can be no 
produce theTffear ” “ a ‘doughty competent cause to 
Starting, at the beginning, Helmholtz assumes the truth 
of Laplace s great conception known as the Nebular Hypo- 
thesis. his theory supposes, as is well known, that at one 
time millions of years ago— the whole of the matter com- 
posing the. various members of the solar system, together 
with any interplanetary substance which may exist, was 
diffused in space in the form of highly rarefied gas. The 
only known cause capable of keeping such materials in such 
a condition is heat, and it is thus further assumed that the 
whole of the heat in our system, together with a large quan- 
tity which has been wasted in space (i.e., space beyond the 
confines of the orbit of Neptune), was stored up in the 
nebulous matter in the form of latent heat. This highly 
laiefied matter gradually radiated its heat into space, and in 
consequence began to diminish in bulk, and at the same 
time to increase in specific gravity. Planets and satellites 
began to form out of it, and the process of cooling and con- 
tiaCbion continued until the system assumed its present 
condition. In this process, assuming the specific heat of 
the condensing matter to be equal to that of water Helm- 
holtz calculates that the heat given out would raise the 
temperature 28,000,000° Centigrade. What, then, has be- 
come of this immense amount of heat ? All of it, except a 
very small fraction, has been radiated into stellar space and 
lost amid the vast recesses which practically exist between 
suns or between the satellites of suns. The small fraction 
has been intercepted by the matter of some of the planetary 
bodies, and its energy, or some portion of it, used up in re- 
arranging the materials of the planet. In this way, perhaps 
the vast store of energy which the deposits of carbonaceous 
matter in the Earth possess, may have been derived from 
the condensation of the nebulous matter, and was employed 
at one time in keeping the molecules of that substance in a 
state of vibration. But the process of condensation havin- 
gone on from the remotest times up to the present does not 
stop here. Helmholtz supposes it to be still going on, and 
m this way he accounts for the heat which we and our 
lellow-worlds derive from the Sun. According to this theory 
the central orb is radiating heat into space at the enormous 
rate indicated at the commencement of this paper, and is 
being cooled by the loss thus experienced. In consequence 
oi this cooling the materials composing the Sun must occupy 
less space, and consequently its diameter become less. 
