7 o6 THE POPULAR SCIENCE MONTHLY. 



in such abundance and under such conditions that it cannot be stored 

 away in the motion of the masses. It is then, probably for the first 

 time, that heat becomes a wave-force, and is radiated into space as 

 light and radiant heat not, however, lost, for that is impossible, but 

 moving ever onward and outward to the day and the place of its final 

 reclamation. 



Our own solar system has already progressed far in this stage of 

 aggregation. All the planets and satellites have become crusted over, 

 and have ceased almost entirely to radiate heat. But the sun, the 

 great central body, the one which should last of all become cold, is 

 still in active combustion or chemical combination. Immense quanti- 

 ties of light and heat are still radiating from its surface so immense 

 that the little fraction which our earth catches as it flies through space 

 gives us all the motion, and life, and beauty, which we enjoy. But 

 the sun is not even now the glowing orb that once it was, as the rock- 

 records of our globe testify. Its bright radiance is slowly but surely 

 fading. Those huge, black incrustations, often twice as large as the 

 whole surface of the earth, that float awhile on its photosphere, and 

 then are suddenly broken up they were not always there. And, if 

 they have grown upon it, the uncomfortable conviction arises that 

 they will continue to grow and darken more and more its life-giving 

 face. Old age is certainly being written on the solar brow. It may 

 be millions of years hence for time is not one of the economies of 

 Nature but the period will surely come when light and heat will all 

 have departed from the sun, as they once ceased to be radiated from 

 the earth and the planets and the numerous stars that have gone out 

 w r ithin the records of astronomy. A pall of darkness will gradually 

 overspread the universe as one by one the stars of the firmament shall 

 fade away and sink into gloomy, lifeless sleep. A day in the mighty 

 calendar of creation has passed, and a night has followed, cold and 

 dark as the tomb of expiring Nature. 



But is there no awakening, no morrow to this night of the uni- 

 verse ? Is the contest over, and never to be renewed '? For answer, 

 let us seek out in this case, as we did once before, the condition and 

 movements of the great contending forces. Those of attraction have 

 now in each world expended their utmost possible energy, and are 

 holding all the forms of matter combined and compacted in a cold 

 and rigid embrace. The forces of repulsion have entirely abandoned 

 the contest, and are either vibrating through the unknown realms of 

 space, or are locked up in the swift and complicated motions of the 

 heavenly bodies. It is probable that by far the greater part of the 

 repulsive forces thus exists in the form of motion. It has been esti- 

 mated, no doubt with a near approximation to truth, that, if by any 

 means the earth co\dd be suddenly arrested in its rapid course, its 

 mass would thereby be raised to the enormous temperature of 23,360 

 Fahr. a heat sufficient to vaporize and dissipate every known sub- 



