ON THE PROBABLE ORIGIN AND AGE OF THE SUN. 



357 



also with the heat which it originally pos- 

 sessed. 



It is therefore evident that if we admit that 

 the nebulous mass .was in a state of incandes- 

 cence prior to condensation, it will really be diffi- 

 cult to fix any limit either to the age of the sun 

 or to the amount of heat which it may have origi- 

 nally possessed. The 20,000,000 years' heat ob- 

 tained by condensation may in such a case be 

 but a small fraction of the total quantity pos- 

 sessed by the mass. 



The question now arises : " By what means 

 could the nebulous mass have become incandes- 

 cent? From what source could the heat have 

 been obtained ? " The dynamical theory of heat 

 affords, as was shown several years ago, 1 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 toward each other with a veloci- 

 ty of 476 miles per second, would by their con- 

 cussion generate in a single moment 50,000,000 

 years' heat. For two bodies of that mass, mov- 

 ing with a velocity of 476 miles per second, would 

 possess 4,149 >< 10 38 foot-pounds of kinetic en- 

 ergy, and this converted into heat by the stop- 

 page 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. 



Why may not the sun have been composed 

 of two such bodies ? And why may not the origi- 

 nal store of heat possessed by him have all been 

 derived from the concussion of these two bodies ? 

 Two such bodies coming into collision with that 

 velocity would be dissipated into vapor and con- 

 verted into a nebulous mass by such an incon- 

 ceivable amount of heat as would thus be gener- 

 ated ; and when condensation on cooling took 

 place, a spherical mass like that of the sun would 

 result. It is perfectly true that two such bodies 

 could never attain the required amount of veloci- 

 ty by their mutual gravitation toward each other. 

 But there is no necessity whatever for supposing 

 that their velocities were derived from their mu- 

 tual attraction alone : they might have been ap- 

 proaching each other with the required velocity 

 wholly independent of gravitation. 



We know nothing whatever regarding the 

 absolute motion of bodies in space ; and, beyond 

 the limited sphere of our observation, we know 

 nothing even of their relative motions. There 

 may be bodies moving in relation to our system 



1 Philosophical Magazine for May, 1863. 



with inconceivable velocity. For anything that 

 we know to the contrary, were one of these 

 bodies to strike our earth the shock might be 

 sufficient to generate an amount of heat that 

 would dissipate the earth into vapor, though the 

 striking body might not be heavier than a can- 

 non-ball. There is, however, nothing very ex- 

 traordinary 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 86 miles of that re- 

 quired. 



It must be borne in mind, however, that the 

 476 miles per second is the velocity at the mo- 

 ment of collision ; but more than one-half of this 

 would be derived from the mutual attraction of 

 the two bodies in their approach to each other. 

 Suppose, for simplicity of calculation, each body 

 to be equal in volume to the sun, and of course 

 one-half the density, the amount of velocity which 

 they would acquire by their mutual attraction 

 would be 274 miles per second. Consequently 

 we have to assume an original or projected ve- 

 locity of only 202 miles per second. And if the 

 original velocity was 676 per second, the total 

 amount of heat generated would suffice for 200,- 

 000,000 years at the present rate of radiation. 



On former occasions 1 I expressed it as my 

 opinion that the total quantity of heat possessed 

 by the sun could not probably exceed 100,000,000 

 years' heat. But if we admit that the heat was 

 derived from motion in space, there really does 

 not seem any reason why it may not be double 

 that amount. 



It will be asked, " Where did the two bodies 

 get their motion ? " It may as well, however, be 

 asked, " Where did they get their existence ? " 

 It is just as easy to conceive that they always ex- 

 isted in motion as to conceive that they always 

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

 which energy can remain in a body without dis- 

 sipation in space. Under other forms a certain 

 amount of the energy is constantly being trans- 

 formed into heat wdiich never can be retrans- 

 formed back again, but is dissipated into space 

 as radiant heat. But a body moving in void 

 stellar space will, unless a collision takes place, 

 retain its energy in the form of motion untrans- 

 formed forever. 



1 Philosophical Magazine, May, 1S6S ; " Climate and 

 Time," chapter x.\i. 



