Jak. 16, 1885.] 



• KNOWLEDGE ♦ 



51 



The Xiglit Sign for the Month. 



ZODIACAL MAPS. 



T"f " E give this week both the day sign and the night sign 

 > T for the month, one showing the zodiacal sign now 

 high in the heavens at midnight, the other showing the 

 region of the zodiac athwart which the sun pursues hi.s 

 course at this part of the year. 



THE SUX'S HEAT.* 



By Richard A. Proctor. 



PROFESSOR YOUNG, of Princeton, in a recent 

 address at Philadelphia, expressed his belief that the 

 contraction theory of the sun's beat is the true and only 

 available theory. I believe so, too, and my object in the 

 present paper is to dwell upon the significance and inte- 

 rest of this remarkable interpretation of the solar 

 mechanism. 



Of course it is known to all that the old theory accord- 

 ing to which the sun's heat is due to combustion (" doubt 

 that the sun is fire," said Shaktspeare, as if the doubt 

 were the quintessence of absurdity) has long since been 

 rejected as futile. A mass of the best combustible mate- 

 ria], equal to the sun in quantity, would Vje burned out at 

 his actual rate of emission — if it could burn right out — 

 in about 5,G00 years. In like manner, the idea of the 

 sun as an intensely hot body simply radiating its heat into 



• From the J^'eic YorJi Trilnne. 



space, as a piece of white hot iron does, without any pro- 

 cess of combustion, has had to be rejected. Even if the sun 

 were formed of matter pcssessing the high sj ecific heat o£ 

 water, which has the remarkable property of giving out 

 more heat in cooling than any other natural substance 

 known (and only one or two artificial sub.'^tances surpass 

 it in this respect), even then ihe sun's emission of heat at 

 his present rate would tot cover more than about 5,500 

 years. Processes of chemical change have been suggested 

 as affording the true source of solar heat ; but they in turn 

 have had to be i ejected as altogether insutiJcient. It is 

 unnecessary to touch on the supposed origin of solar heat 

 in the gathering in of meteoric bodies; for in reality tliisf 

 process belongs to the contraction theory ; it has, however^ 

 been abundantly demonstrated that the actual amount of 

 sun heat which could be derived from the drawing in of 

 matter now outside the solar globe can be but very small. 

 We are left, in fine, no resource — so far as our present 

 knowledge extends — but to regard the process of contrac- 

 tion taking place within the solar globe as the true source 

 of all or very nearly all the heat and light which the sun 

 emits, and therefore of every form of force and life on this 

 earth and on whatever other members of the solar systen> 

 may be the abode of life, or a scene of the display of any 

 forms of force not derived from internal heat and energy. 



But now, at the very outset, what a mighty mystery is 

 thus unveiled ! It seemed wonderful enough to recognise 

 in what we fondly call inert matter the source of the 

 energies which guide the heavenly bodies in their motions. 

 I know indeed ni thing more mysterious (more hopelessly 



