Jan. ro, 1878] 



NATURE 



207 



July, 18; 7) I have proved from geological evidence that 

 the antiquity of our habitable globe must be at least three 

 times greater than it could possibly be had the sun 

 derived its heat simply from the condensation of its mass. 

 This proves that the gravitation theory of the origin of 

 the sun's heat is as irreconcilable with geological facts as 

 it is, according to Haeckel, with those of evolution, and 

 that there must have been some other source, in addition, 

 at least, to gravity, from which the sun derived his store 

 of energy. 



That other source is not so inconceivable as has been 

 assumed, for it is quite conceivable that the nebulous mass 

 from which the sun was formed by condensation might 

 have been possessed of an original store of heat previous 

 to condensation. And this excessive temperature may be 

 the reason why the mass existed in a nebulous orrareSed 

 condition. Now if the mass were originally in a heated 

 condition then in condensing it would have to part not 

 merely with the heat of condensation, but also with the 

 heat it originally possessed. 



The question then arises— By what means could the 

 nebulous mass have become incandescent ? From what 

 source could the heat have been obtained 1 The dynami- 

 cal theory of heat affords, as was shown several years 

 ngo {Phil. Mag. for May,. 1 868), an easy answer to this 

 question. The answer is that the energy in the form of 

 heat possessed by the mass may have been derived from 

 motion in space. Two bodies, each one-half the mass of 

 the sun, moving directly towards each other with a 

 velocity of 476 miles per second, would, by their concus- 

 sion, generate in a simple moment 50,000,000 years' heat. 

 For two bodies of that mass, moving with a velocity of 

 476 miles per second, would possess 4,149 X lo^* foot- 

 pounds of kinetic energy, and this, converted into heat 

 by the stoppage of their motion, would give out an 

 amount of heat which would cover the present rate of 

 the sun's radiation for a period of 50,000,000 years. 



There is nothing very extraordinary in the velocity 

 which we have found would be required to generate the 

 50,000,000 years' heat in the case of the two supposed 

 bodies. A comet having an orbit extending to the path 

 of the planet Neptune, approaching so near the sun as to 

 almost graze his surface in passing, would have a velocity 

 of about 390 miles per second, which is within eighty- six 

 miles of that required. 



It must be borne in mind, however, that the 476 miles 

 per second is the velocity at the moment of collision. 

 But more than one-half of this velocity, or 274 miles per 

 second, would be derived from their mutual attraction as 

 they approached each other. We have consequently to 

 assume an original or projected velocity of only 202 miles 

 per second. If the original velocity was 678 per second, 

 this, with the 274 derived from gravity, would generate 

 an amount of heat which would suffice for 200,000,000 

 years. And if we assume the original velocity to have 

 been 1,700 miles per second, an amount of heat would 

 be generated in a single moment which would suffice for 

 no less than 800,000,000 years. 



It will be asked. Where did the two bodies get their 

 motion 1 It may as well, however, be asked, Where did 

 they get their existence ? It is just as easy to conceive 

 that they always existed in motion as that they always 

 existed at rest. In fact, this is the only way in which 

 energy could remain in a body without dissipation into 

 spa^e. Under other forms a certain amount of it is con- 

 stantly being transformed into heat which never can be 

 retransformed back again, but is dissipated into space as 

 radiant heat. But a body moving in void stellar space 

 will retain its energy in the form of motion undiminished 

 and untransformed for ever, unless a collision takes place. 



The theory that the sun's heat was originally derived 

 from motion in space is, therefore, for this reason, also 

 more in harmony with evolution than the gravitation 

 theory, because it explains how the enormous amount of 



energy which is being dissipated into stellar space may 

 have existed in the matter composing the sun untrans- 

 formed during bygone ages. Or in fact for as far back 

 as the matter itself existed. 



In conclusion there are only two sources conceivable 

 from which the sun could have derived his heat. The 

 one \'i gravitation, the other motion in space. The former 

 could have afforded only about 20,000,000 or 30,000,000 

 years' heat, but there is in reality no absolute limit to the 

 amount which may have been derived from the latter 

 source, for the amount generated would depend on the 

 velocity of motion. And when we take into consideration 

 the magnitude of the stellar universe, the difference between 

 a motion of 202 miles per second, and one of 1.700 miles 

 to a great extent disappears, and the one velocity becomes 

 about as probable as the other. 



It may be urged as an objection to the theory that we 

 have no experience of bodies moving in space with such 

 enormous velocities as the above. This objection, for the 

 following reason, is of no weight. 



No body moving with a velocity exceeding 400 miles 

 per second could remain a member of our solar system ; 

 and beyond our system there is nothing visible but the 

 stars and nebulae. These stars, however, are suns like 

 our own, and visible because, like the sun, they have 

 lost their motion — the lost motion being the origin 

 of their light and heat. Bodies moving in stellar space 

 with these enormous velocities can have neither light 

 nor heat, and, of course, must be invisible to us. Ttiey 

 must first lose their motion before the kinetic energy in 

 the form of motion can be transformed into light and 

 heat, so as to constitute visible suns. 



James Croi.l 



ON THE FORMATION -OF HAILSTONES, 

 RAINDROPS, AND SNOWFLAKES^ 



HP HE author commences by recapitulating some of the 

 -»• leading points in a paper which he read before the 

 same Society on October 31, 1876, "On the Manner in 

 which Raindrops and Hailstones are Formed." In this 

 paper, which was published in Nature (vol. xvi. p. 163), 

 he had shown that the aggregation of the small cloud par- 

 ticles into raindrops or hailstones is sufficiently accounted 

 for by the fact that the larger pirticles descend faster 

 than the others, and consequently overtake those imme- 

 diately beneath them, and, combining with these, form 

 still larger particles, which move with greater velocity, 

 and more quickly overtaking the particles in front of 

 them, add to their size at an increasing rate. He also 

 showed that the shape and structure of ordinary hail- 

 stones was exactly such as would result from this manner 

 of formation. For he had observed that the shape of 

 hailstones was not as it at first sight appeared, that of 

 more or less imperfect spheres, but that of more or less, 

 imperfect cones or pyramids with rounded bases, the 

 conical surfaces being striated, the striae radiating from 

 the vertex ; the texture being that of an aggregation of 

 a number of small ice particles without crystailme form, 

 being packed more closely together toward the base or 

 rounded face of the stone. In this paper the author had 

 reverted to the possibility of making artificial hailstones 

 by blowing a stream of frozen fog against a small object, 

 making, as it were, the cloud to rise up and meet the 

 stone, instead of the stone falling through the cloud. 



He had not, however, then overcome the difficulty of 

 obtaining such a stream of frozen fog, but gave two 

 sketches of plaster stones, which, as far as their shape 

 and the striated appearance of their surface were con- 

 cerned, closely resembled hailstones, and which plaster 

 stones had been obtained by blowing some finely-divided 



I Abstract of paper by Prof Osborre Reynolds, F.R.S, read at the 

 Manchester Literary and Philosophical Society. 



