HEAT. 69 



of the celestial bodies may again, from changes in their 

 positions, vary through epochs which are of enormous dura- 

 tion as regards the existence of the human species ; and 

 while some are giving off heat, others, differently constituted, 

 may be absorbing it. Mr. Matthieu Williams has suggested 

 that the sun, in its motion through space (a motion of which 

 there is now tolerably good evidence), condenses and brings 

 within the range of chemical affinity and combustion the 

 attenuated matter which fills the interplanetary spaces. As 

 to whether this view will turn out to be well-founded or not it 

 would be premature to express an opinion. That the change 

 of position of the sun in space may produce some effect of 

 condensation or friction on the interplanetary medium and on 

 meteoric bodies interspersed through it, seems not impro- 

 bable ; and however visionary conjectures on the illimitable 

 universe may be, the notion that the universe is gradually 

 equalising its heat and tending to a chaos of uniform tem- 

 perature and equilibrium of force, although it may be sup- 

 ported by the phenomena we see immediately around us, 

 seems to me like those views of the instability of the solar 

 system which Laplace negatived, and would require far more 

 cogent proof than any at present given. Though the whole 

 subject will probably never be grasped by human intelligence, 

 enlarged observation may prove that phenomena seeming to 

 tend in one direction will turn out to be recurrent, though never 

 absolutely identical in their recurrence : that there is, through- 

 out the universe, gradual change but no finality. 



The views of Laplace, adopted by many, supposed the 

 planets to have been formed by a gradual condensation of 

 nebulous matter. A modification of this view might, perhaps, 

 be suggested, viz. that worlds or systems, instead of being 

 created as wholes at definite periods, are gradually changing 

 by atmospheric additions or subtractions, or by accretions or 

 diminutions arising from nebulous substance or from meteoric 

 bodies, so that no star or planet could at any time be said 

 to be created or destroyed, or to be in a state of absolute 

 stability, but that some may be increasing, others dwindling 

 away, and so throughout the universe, in the past as in the 

 future. When, however, questions relating to cosmogony, or 



