1881.] from the time of Newton. 135 



much after the same manner that vapours are condensed into 

 water, or exhalations into grosser substances, though not so easily 

 condensible ; and after condensation wrought into various forms, at 

 first by the immediate hand of the Creator, and ever since by the 

 power of nature, which, by virtue of the command ' increase and 

 multiply,' became a complete imitator of the copy set her by the 

 great Protoplast. Thus, perhaps may all things be originated from 

 ether." 



If now we look to the third book of the Principia, we shall find 

 in proposition 41 the remarkable chemical argument by which 

 Newton was led to regard the interstellary ether as affording " the 

 material principle of life" and "the food of planets." Consider- 

 ing the exhalations from the tails of comets, he supposes that the 

 vapours thus derived, being rarified, dilated, and spread through the 

 whole heavens, are by gravity brought within the atmospheres of 

 the planets, where they serve for the support of vegetable life. 

 Inasmuch moreover as all vegetation is supported by fluids, and 

 subsequently by decay is, in part, changed into solids, by which the 

 mass of the earth is augmented, he concludes that if these essential 

 matters were not supplied from some external source, they must 

 continually decrease, and at last fail. This vital and subtile part of 

 our atmosphere, so important, though small in amount, he then 

 supposed might come from the tails of comets 1 . 



This appeared in the first edition of the Principia, in 1687. 

 It was not until later that the conception of exhalations from other 

 celestial bodies took shape in the mind of Newton, as we can learn 

 from the Optics. Thus, in the first edition of this work, in 

 Query 11, the sun and fixed stars are spoken of as great earths, 

 intensely heated, and surrounded with dense atmospheres which, by 

 their weight, condense the exhalations arising from these hot. 

 bodies. To this Query is added in 1706 the suggestion that the 



1 "Vapor enim in spatiis illis liberrimis perpetuo rarescit, ac dilatatur. Qua 

 ratione tit ut cauda omnis ad extremitatem superiorem latior sit quam juxta capita 

 cometae. Ea autem rarefactione vaporem perpetuo dilatatum diffundi tandem, et 

 spargi par coelos universos, deinde paulatim in planetas per gravitatem suam attrahi 

 et cum eorum atmosphaeris misceri, ratione consentaneum videtur. Nam quem- 

 admodum maria ad constitutionem Terrae hujus omnino requiruntur, idque ut ex iis 

 per calorem Solis vapores copiose satis excitentur, qui vel in nubes coacti decidant 

 in pluviis, et Terram omnem ad procreationem vegetabilium irrigent et nutriant ; 

 vel in frigidis montium verticibus condensati (ut aliqui cum ratione philosophantur) 

 decurrant in fontes et fiumina: sic ad conservationem marium et humorum in 

 planetis requiri videntur cometae ex quorum exhalationibus et vaporibus conden- 

 satis, quicquid liquoris per vegetationem et putrefactionem consumitur, et in 

 Terram aridam convertitur, continud suppleri et refici possit. Nam vegetabilia 

 omnia ex liquoribus omnino crescunt, dein magna ex parte in Terram aridam per 

 putrefactionem abeunt, et limus ex liquoribus putrefactis perpetuo decidit. Hinc 

 moles Terrae aridae indies augetur, et liquores, nisi aliunde augmentum sumerent, 

 perpetuo decresere deberent, ac tandem deficere. Porro suspicor spiritum ilium, qui 

 aeris nostri pars minima est, sed subtillissima et optima, et ad rerum omnium vitam 

 requiritur, ex cometis praecipue venire." — Newton, Principia, lib. III. prop. xli. 



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