66 HABIT AND INTELLIGENCE. [chap. 



of the bodies formed out of it, to rotate. But the nebulous 

 mass out of which the solar system has condensed was in 

 all probability only an infinitesimally small part of the 

 original nebula, which, though perhaps not actually infinite, 

 was probably the origin of the whole starry system known 

 to us. The first condensation of a nebulous mass produces, 

 not globular, but very irregular forms : we see these in 

 those parts of the original nebula that still remain as 

 nebulae : the motions due to the mutual attractions of 

 irregular forms will be very complex, and will be further 

 complicated by the resistance of the rarer medium to the 

 motion of the denser aggregations. Our mathematics are 

 utterly inadequate to predict what such motions would be, 

 but we may safely assert that most of them, if not all, will 

 be pai-tly rotatory; and the law of the conservation of 

 rotation will be satisfied by the rotations in opposite 

 directions compensating each other, so that their algebraic 

 sum will be nothing. 

 Solar radi. With the sniall exceptions of volcanic action and of 

 OTeat mo- the tides, all the motions on the surface of the earth have 

 tive power, their motive power in solar radiance. It is this which sets 

 the winds, the rain, tlie rivers, and the ocean currents in 

 motion ; and it is the motive power also of animal and 

 vegetable life ; for the heat and motor energy of all living 

 beings is due to the combustion of carbon and hydrogen, 

 and the potential energy Avhich becomes actual in that 

 combustion is the transformed energy of the solar radiance 

 that has fallen on living vegetables. The same is true of 

 the heat given out by the combustion of coal: it is the 

 transformed radiance of the sun, which, millions of years 

 ago, fell on the pines and ferns of the coal formations, 

 decomposed the carbonic acid of the air, and in doing 

 so was transformed into the potential energy due to the 

 separation of the carbon from the oxygen ; which energy 

 reappears as heat in every coal fire.^ 

 The tides. This, of course, is not true of tidal action. The 

 motive power of the tides is not solar heat, nor any heat 



1 Tyndall on Heat as a Mode of Motion, p. 430. This subject is to be 

 further explained in the chapter on Vital Energy. 



