182 Review of Recent Geological Literature. 
tion to allow the imagination to run riot is great. Its value in physi- 
cal investigations cannot be overestimated, yet it should never be the 
blind flounderings of an untaught and untamed imagination, but rath- 
er the advanced thought of clear minds, guided by known principles, 
out-running for the time the slower processes of demonstration, but 
always returning to verify preconceived theories by sound reasoning 
or actual experiment." , 
The author hinges his reasoning on three postulates, viz. : (1) In- 
finite duration of time in the past. (2.) Infinite extension of the uni- 
verse in space, peopled with suns, worlds, comets and nebulee. (3.) 
Conservation of force or energy. 
The various prominent theories for the cause of the sun's heat are 
briefly considered and are severally found to be defective and unsatis- 
factory, viz : 
First, The conflagration theory, is untenable because if the universe 
has existed through past eternity the sun, no matter what his size or 
material, would have been burnt out, or oxidized millions of ages ago ; 
because, also, it is known that the temperature of the sun is too high 
for combustion, and because, further, if it were possible to add millions 
of tons of coal to the sun it would undergo rarefaction instead of con- 
densation, and hence would produce cold rather than heat. 
Second, The meteoric theory is brought to encounter nine obstacles 
which are categorically presented, (a) It is unproved. (b) The 
theory indicates only a temporary provision, since the meteors would 
all be absorbed in time by our sun and the other suns, and the solar 
fires would ultimately die out for want of fuel, (c) Owing to the con- 
tinued increase of the mass of the sun its power of attraction would in- 
crease and it would cause the narrowing of the orbits of the planets, 
so that it would only be a question of time when it would absorb the 
earth and all the members of our system, (d) Small meteors, mov- 
ing in regular orbits, according to Newtonian laws, may collide with 
the earth when in nearly the same plane, but it is an impossibility for 
them to bolt from their orbits and fall upon the sun. (e) The theory 
requires the acceptance of the unproved assumption that space through 
which the sun and solar system are moving is filled with wandering 
meteors — meteors utterly unlike the minute bodies which are unable 
to penetrate even our thin atmospheric envelope, but more nearly re- 
sembling the moon or the inferior planets in size. If such masses are 
falling like hail on the sun, they should fall as thick and fast on the 
earth in proportion to its size, and then the earth would become as hot 
as the sun, and would be in danger of being dislodged from her orbit, 
(f) The efi'ect of a collision of a meteor with the sun can only be 
judged by comparison with such collisions with the earth. Hence the 
collision of a non-elastic meteor with the elastic gaseous envelope of 
the sun might, by the arrested motion, develope heat enough to raise 
the cold mass of the meteor to the same temperature as that of the 
sun, and the temperature of the sun would neither be increased nor di- 
