7 02 THE POPULAR SCIENCE MONTHLY. 



at some future age they will doubtless present a single side to the 

 sun, as our moon, from similar causes, now does to the earth. 



Furthermore, it is thought that the medium which conveys li^ht 

 through space, extremely attenuated though it may be, is capable of 

 opposing some resistance to planetary movements, so that the sun 

 may at last unite with itself all the orbs now circling around it. The 

 collision between the sua and its worlds would render the whole mass 

 fiery hot ; but radiation, in the course of time, would slowly bring its 

 temperature lower and lower, until it would cease to shine altogether. 

 The theory then supposes that the fate which shall have overtaken 

 the solar system will then attack the sidereal heavens; that the 

 causes which shall first make the planets unite with their primary 

 will make stars unite with one another, until the ultimate result of 

 all these changes may be that a solitary gigantic ball shall contain all 

 the matter now interfused through space, its enormous store of en- 

 ergy, in the form of equably-diffused heat, being incapable of further 

 change, and utterly unfit for the production or maintenance of life. 



All this is assuredly very bold, and deduced most fairly from its 

 premises ; but premises in truth and completeness are of much more 

 account and far more difficult of discovery than methods of logical 

 inference. Let us briefly examine the grounds on which it is sup- 

 posed that Nature is doomed to a death without resurrection, and see 

 if they warrant the tremendous conclusions drawn from them. 



The theory illustrates very pointedly the difficulties in which the 

 finite mind of man becomes involved when it attempts to deal with 

 what is not thinkably finite or, if the term be preferred, infinite. In 

 the first place, the theory under consideration assumes the finiteness 

 in amount of matter and motion ; but we do not know, nor can we 

 imagine, that space has bounds, neither can we limit the extent of the 

 orbs and movements which, as far as we can see, occupy it. 



Secondly, the theory makes another conjecture in the realm of the 

 absolute, when it presumes that heat is an absolutely homogeneous 

 motion that particles endowed with it move with so perfect a uni- 

 formity that there is an exclusion of any difference of motion which 

 might serve as a starting-point for mechanical changes. But has 

 science advanced far enough to make such a proposition tenable ? Our 

 knowledge of the ultimate structure of matter is very restricted ; and 

 as to what the modes of motion are which we call heat, electricity, 

 and so on, we are entirely in the dark. Their quantities we know, but 

 their qualities, their peculiar orbits, have scarcely been guessed at as 

 yet. From a variety of reasons, however, the modern opinion, like 

 the ancient one, is that matter is made up of atoms, which in the cir- 

 cumstances are units even if ideally divisible. Approximate measure- 

 ments of them have been made by Prof. Sir William Thomson him- 

 self. [See his paper in Nature, vol. L, p. 551.) 



Now, if atoms by virtue of their heat moved uninterruptedly in a 



