POPULAR SCIENTIFIC LECTURES. 



631 



Heaving M>1 weaving 



The ehaogM of life. 

 At the whirling loom of time unawcd, 

 I work the living mantle of God. 



Let ns return to the special question which 

 concerns us here : Whence does the sun de- 

 rive this enormous store of force which it 

 nends out ? 



On earth the processes of combustion arc 

 the most abundant source of heat. Does 

 the sun's heat originate in a process of this 

 kind ? To this question we can reply with 

 a complete and decided negative, for we now 

 know that the sun contains the terrestrial 

 elements with which we arc acquainted. 

 Let us select from among them the two, 

 which, for the smallest mass, produce the 

 greatest amount of heat when they combine ; 

 let us assume that the sun consists of hydro- 

 gen and oxygen, mixed in the proportion in 

 which they would unite to form water. Tho 

 mass of the sun is known, and also the quan- 

 tity of heat produced by the union of known 

 weights of oxygen and hydrogen. Calcula- 

 tion shows that under the above supposition, 

 the heat resulting from their combustion 

 would be siifficient to keep up the radiation 

 of heat from the sun for 3021 years. That, 

 it is true, is a long time, but even profane 

 history teaches that the sun has lighted and 

 warmed us for 3000 years, and geology puts 

 it beyond doubt that this period must be ex- 

 tended to millions of years. 



Known chemical forces are tHus so com- 

 pletely inadequate, even on the most favor- 

 able assumption, to explain the production 

 of heat which takes place in the sun, that we 

 must quite drop this hypothesis. 



We must seek for forces of far greater 

 magnitude, and these we can only find in 

 cosmical attraction. We have already seen 

 that the comparatively small masses of 

 shooting-stars and meteorites can produce 

 extraordinarily large amounts of heat when 

 their cosmical velocities are arrested by our 

 atmosphere. Now the force which has pro- 

 duced these great velocities is gravitation. 

 We know of this force as one acting on the 

 surface of our planet when it appears as ter- 

 restrial gravity. We know that a weight 

 raised from the earth can drive our clocks, and 

 that in like manner the gravity of the water 

 rushing down from tho mountains works our 

 mills. 



If a weight falls from a height and strikes 

 the ground its mass loses, indeed, the visible 

 motion which it had as a whole in fact, 

 however, this motion is not lost ; it is trans- 

 ferred to the smallest elementary particles of 

 the mass, and this invisible vibration of the 

 molecules is the motion of heat. Visible 

 motion is transformed by impact into the 

 motion of heat. 



That which holds in this respect for grav- 

 ity, holds also for gravitation. A heavy 

 mass, of whatever kind, which is suspended 

 in space separated from another heavy moss, 

 represents a force capable of work. For 

 both masses attract each other, and, if un- 

 restrained by centrifugal force, they move 



toward each other under the influence of 

 this attraction ; this takes place with ever- 

 increasing velocity ; and if this velocity is 

 finally destroyed, whether this be suddenly, 

 by collision, or gradually, by the fnction of 

 movable parts, it develops the corresponding 

 quantity of the motion of heat, the amount 

 of which can be calculated from the equiva- 

 lence, previously established, between heat 

 and mechanical work. 



Now we may assume with great probability 

 that very many more meteors fall upon tht) 

 sun than upon the earth, and with greater 

 velocity, too, and therefore give more heat. 

 Yet the hypothesis, that the entire amount 

 of the sun's heat which is? continually lost by 

 radiation, is made up by tha fall of meteors, 

 a hypothesis which was propounded by 

 Mayer, and has been favorably adopted by 

 several other physicists, is open, according 

 to Sir W. Thomson's investigations, to ob- 

 jection ; for, assuming it to hold, the mass 

 of the sun should increase so rapidly that the 

 consequences would have shown theuiselven 

 in the accelerated motion of the planets. 

 The entire loss of heat from the sun cannot 

 at all events be produced in this way ; at tha 

 most a portion, which, however, may not be 

 inconsiderable. 



If, now, there is no present manifestation 

 of force sufficient to cover the expenditure 

 of the sun's heat, the min must originally 

 have had a storo of heat which it gradually 

 gives out. Bat whenca this store? W 

 know that the cosmical forces alone oould 

 have produced it. And here the hypothesis, 

 previously discussed an to the origin of the 

 sun, comes to our aid. If the mass of the 

 sun had been once diffused in cosmical space, 

 and had then been condensed that is, had 

 fallen together under the influence of celes- 

 tial gravity if then the resultant motion 

 had been destroyed by friction and impact, 

 with the production of heat, the new world 

 produced by such condensation must have 

 acquired a store of heat not only of consider- 

 able, but even of colossal, magnitude. 



Calculation shows that, assuming the 

 thermal capacity of the sun to be the same as 

 that f water, the temperature might be 

 raised to 28,000, 000 of degrees, if this quan- 

 tity of heat could over have been present in 

 the sun at one time. This cannot be 

 assumed, for such an increase of temperature 

 would offer the greatest hindrance to con- 

 densation. It is probable rather that a great 

 part of this heat, which was produced by 

 condensation, began to radiate into space 

 before this condensation was complete. But 

 the heat which the nun could have previously 

 developed by its condensation, would have 

 been sufficient to cover its present expendi- 

 ture for not less than 22,000,000 of years of 

 the past. 



Aad the sun is by no moans so dense as 



it may become. Spectrum analysis demon* 

 strates the presence of largo masses of iron 

 and of other known constituents of the rocks. 

 The pressure which endeavors to condense 

 the interior is about 800 times us great as 



