252 C. Lloyd Morgan — Physiography. 



contraction. And as it contracted it left behind it rings of vapour 

 which, breaking up, formed secondary rotating spheroids, themselves 

 contracting, themselves leaving behind them rings, forming tertiary 

 spheroids, themselves passing in their orbits round the central mass. 

 That central spheroid mass is the Sun ; one of the secondary rotating 

 spheroids is the Earth, the Moon being a tertiary spheroid. The 

 Earth-planet thus formed was gaseous ; but as time rolled on, it 

 passed through the liquid state, to the more or less solid state, which 

 it at present possesses. 



Sun-heat is therefore the result of the condensation of the primary 

 spheroid : earth-heat the remnant of that produced by the condensa- 

 tion of a secondary nebulous spheroid. 



And now comes the question, how was the rotating nebulous 

 spheroid formed ? 



If we take a small piece of lead and deal it a number of heavy 

 blows with a hammer, we shall find that the lead becomes hot. If 

 we continue to hammer for ten minutes, we shall find that the lead 

 becomes too hot to hold. Now what is the cause of the heating of 

 the lead. Simply this : when the lead is struck, the motion of 

 the hammer is suddenly stopped : but the motion is taken up in a 

 new form by the particles of the lead, and this new form of motion 

 is heat. The visible motion of the hammer is converted into the 

 invisible molecular motion of heat : for heat is simply the rapid 

 vibration of the ultimate particles of matter. 



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 Inflexible. It is 

 quite conceivable that a shot or bullet of lead might be projected 

 with such violence as to be, not only fused, but converted into vapour 

 on striking the target. For when the motion of heat becomes ex- 

 tremely violent, the particles of matter are shaken asunder, and 

 a vapour 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 19 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 vapour. " 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. CroU and others (and here, be it 

 noticed, we pass to the still less known : to the purely hypothetical, 

 but still conceivable), that the nebulous mass from which the solar 

 system has been evolved resulted from the collision in space of two 



