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XXXI. Molecular Attraction. By Frederick D. Brown, 

 J3.Sc, Demonstrator of Chemistry in the University Museum, 

 Oxford*. 



AMONG those who are interested in chemical science, and 

 especially those who are engaged in an attempt to 

 advance that science by experimental work, there must be 

 many who feel that, notwithstanding the immense number of 

 new facts brought forward during recent years, comparatively 

 little real progress has been made. Since 1857, when Kekule 

 first published his views concerning the internal construction 

 of the molecules, chemists have been mainly occupied in ap- 

 plying his ideas to a multitude of carbon compounds. This 

 work, although of the greatest importance, has led us perhaps 

 too much into questions of detail, and has turned away our 

 attention from the other great problems which were of so 

 much interest to our predecessors. The chemical literature 

 of the past decade is replete with information concerning 

 the reactions undergone by complicated organic substances ; 

 but it rarely tries to tell us how and why these reactions take 

 place. We diligently gather stores of stones for our building ; 

 and, this done, we are too often content to stand listlessly 

 round the heaps waiting for the builder, and leaving even the 

 work of the stonemason to the chances of the future. If, 

 under these circumstances, any one tries, in however feeble a 

 fashion, to arrange a few of the stones together, the work will 



in Newton's famous Hypothesis touching his Theory of Light and Colour, 

 in his subsequent letter to Boyle in 1679, and also in the Queries 18-24 

 appended to Book III. of his l Optics/ in all of which the various pheno- 

 mena are ascribed to a supposed setherial medium. From various consi- 

 derations it appears probable that these Queries, though first published 

 in 1717, were indited before the Principia, which was written in 1685- 

 86, and published in 1687 ; while the General Scholium itself did not 

 appear till the second edition of the Principia, in 1 713. 



In this connexion it may be noticed that the uncertain and obscure 

 utterances foimd both in Newton's essay of 1675 and in the Queries to 

 the ' Optics/ with regard to exhalations from the sun and other celestial 

 bodies, were, after his studies of the comet of 1680, exchanged for the 

 clearly-defined opinions in Propositions 41 and 42 of the third book of 

 the Principia. In these it is maintained that the exhalations alike from 

 the sun, the fixed stars, and the tails of comets, are not only diffused 

 throughout all space, and finally reach the atmospheres of the planets, 

 but that the matters thus conveyed are necessary for the maintenance 

 of vegetable life, and contribute to the solid mass of the earth. These 

 views were a remarkable anticipation of some of the conclusions announced 

 by the present writer in 1878, and later in 1880, in an essay " on the 

 Chemical and Geological Relations of the Atmosphere," for which see 

 the ' American Journal of Science ' for May 1880. 



* Communicated by the Author. 



