13° 
[March, 
The Heat of the Sun. 
pass quite close to him, and therefore through 
without suffering any loss of energy- P 
fore come to the conclusion that the heat of the bun was 
produced in this way, but is not thus matmained 
aiders “ the low rate of cooling, and consequent constancy 
of the emission, is due to the h.gh spe infctad o the ™ 
tpriaU of which the Sun is composed. — (iyndaii.; mu 
cooling down ; but a. enormous rate 
at which he gives out heat, according to oui knowiea e o 
terrestrial things, we should imagine he would soon be 
burnt out. But this notion, if it exists, must be dispelled 
as Thompson proves that the heat thus origins y - pro 
is able to supply the Sun with sufficient to last him toi no 
16 Bu^aUhouT'd°e“mg a with small masses of matte, this 
theory ii Ho* confined fo them. The heat may be produced 
by larger masses striking the Sun. In e ils ^ • u y 
nomical observations we have it set d° wn t h a t ^casro nally 
stars are observed to suddenly increase in bn ^ ianc y 
they reach a maximum, and then to decline un y 
their former brightness. Thus in 1572 an entne y . 
suddenly “ appeared in the constellation Cassiopeia, a 
gradually increased in brilliancy until it surpassed all the 
other stars. It could be plainly seen m the 1 day time On a 
sudden, November nth, it was as bright as Venu a : h 
brightest. In the following March it was o he first ^mag 
nitude. It exhibited various hues 1 of wlour £ * ce 
months, and disappeared in Maich, I 574- ( P These 
then many similar occurrences have been noted, in 
can only be satisfactorily explained by supposmg a colhs o 
between two bodies to have occurred. Afting upon this id 
Sir W Thomson has calculated the heat which would be 
given out by the various bodies composing the p ane > 
svstem° falling into the Sun. The table is as follows, the 
heat being expressed as able to sustain the solai emission 
for the stated times 
Mercury ... ... 
Venus 
Earth . 
Mars . 
Jupiter.. 
Saturn .. 
Uranus 
Neptune 
83 
94 
12 
32'240 
9659 
1610 
1890. 
6 years 214 days. 
) 5 
227 „ 
303 » 
252 „ 
