680 Phystography. [ October, 
When a bullet is shot from a rifle against an iron target, the 
rapidity of the motion is suddenly arrested; heat is developed ; 
and this heat may in some cases be sufficient to melt the point of 
the bullet. In the same way the immense iron shot, hurled from 
our modern pieces of ordnance, cannot fail to be intensely heated, 
when they strike against the sides of such a ship as the /uflexible. 
It is quite conceivable that a shot or bullet of lead might be pro- 
jected with such violence as to be, not only fused, but converted 
into vapor on striking the target. For when the motion of heat 
becomes extremely violent, the particles of matter are shaken 
asunder, and a vapor is formed. 
We may take the velocity of a rifle bullet to be 225 feet in a 
second. The velocity at which the earth moves through space, 
as she travels round the sun, is about nineteen miles in a second. 
If we imagine that the earth were suddenly to strike a huge 
target, the heat generated would be sufficient, not only to fuse 
the earth, but to reduce it in great part to vapor. “The amount 
of heat thus developed would be equal to that derived from the 
combustion of fourteen globes of coal, each equal to the earth in 
magnitude. And if, after the stoppage of her motion, the earth 
should fall into the sun, as it assuredly would, the amount of heat 
generated by the blow would be equal to that developed by the 
combustion of 5600 worlds of solid carbon.” 
Now, it is supposed by Dr. Croll and others (and here, be it 
noticed, we pass to the still less known; to the purely hypothe- 
tical, but still conceivable), that the nebulous mass from which the 
solar system has been evolved resulted from the collision in space 
of two vast masses moving at great velocity. Each of these 
masses may be supposed to have developed from a -nebulous 
mass, in the same way that the solar system has itself developed. 
Such nebulous masses were endowed with that high form of 
_ energy, which may be termed, generally, the energy of separation. 
But we have seen that this and all other intermediate forms of 
energy tend to run down, and be degraded to heat uniformly 
distributed throughout space. Some men of science tell us that 
this will be the ultimate condition of the energy of the universe. 
They tell us that the planets will fall into the sun, and that thus 
ee the matter of the solar system will be aggregated into one mass, 
that this mass coming into collision with another mass similarly 
ormed will produce the nebulous spheroid from which another 
