30 



SCIENCE. 



[N. S. Vol,. I. No. 2. 



whole region is apparent. In that case the 

 border kind is whollj' a human conception 

 of which nature talies no cognizance, and 

 so it is with the scientific border land to 

 which I propose to invite your attention 

 this evening. 



To the popular mind there are no two 

 sciences further apart than astronomj' and 

 geology. The one treats of the structure 

 and mineral constitution of our earth, the 

 causes of its physical features and its his- 

 torj', while the other treats of the celestial 

 bodies, their magnitudes, motions, distances, 

 periods of revolution, eclipses, order, and of 

 the causes of their various phenomena. 

 And yet many, perhaps I maj^ even say 

 most of the apparent motions of the heavenly 

 bodies are merely reflections of the motions 

 of the earth, and in studjdng them we are 

 really studying it. Furthermore, preces- 

 sion, nutation and the phenomena of the 

 tides depend largely upon the internal struc- 

 ture of the earth, and there astronomy and 

 geology merge into each other. Neverthe- 

 less the methods of the two sciences are 

 widely different, most astronomical prob- 

 lems being discussed qiiantitatively bj' 

 means of rigid mathematical formulre, while 

 in the vast majority of cases the geological 

 ones are discussed only qualitatively, each 

 author contenting himself with a mere state- 

 ment of what he thinks. With precise data 

 the methods of astronomy lead to verj' exact 

 results, for mathematics is a mill which 

 grinds exceeding fine ; but, after all, what 

 comes oiit of a mill depends wholly upon 

 what is put into it, and if the data are un- 

 certain, as is the case in most cosmological 

 problems, there is little to choose between 

 the mathematics of the astronomer and the 

 guesses of the geologist. 



If we examine the addresses delivered by 

 former presidents of this Association, and of 

 the sister — perhaps it would be nearer the 

 truth to say the parent — ^Association on the 

 other side of the Atlantic, we shall find 



that they have generally dealt either with 

 the recent advances in some V)road field of 

 science, or else with the development of 

 some special subject. This evenmg I pro- 

 pose to adopt the latter course, and I sliall 

 invite your attention to the present condi- 

 tion of our knowledge respecting the magni- 

 tude of the solar system, but in so doing it 

 will be necessary to introduce some con- 

 siderations derived from laboratory experi- 

 ments upon the luminiferous ether, others 

 derived from experiments upon ponderable 

 matter, and still others relating both to the 

 surface phenomena and to the internal 

 structure of the earth, and thus we shall 

 deal largely with the border land where 

 astronomy, pthysics and geology merge into 

 each other. 



The relative distances of the various 

 bodies wliich compose the solar sj'stem can 

 be determined to a considerable degree of 

 approximation with very crude instruments 

 as soon as the true plan of the system be- 

 comes known, and that plan was taught by 

 Pj-thagoras more than five hundred years 

 before Christ. It must have been knoA\Ti to 

 the Egyptians and Chaldeans still earlier, if 

 P3i:hagoras really acquired his knowledge 

 of astronomy from them as is affirmed by 

 some of the ancient WTiters, but on that 

 point there is no certaintj^ In public Pj-tha- 

 goi-as seemingly accepted the current belief 

 of his time, which made the earth the center 

 of the universe, but to his own chosen dis- 

 ciples he communicated the true doctrine 

 that the sun occupies the center of the 

 solar system, and that the earth is onlj' one 

 of the planets revolving around it. Like 

 all the world's greatest sages, he seems to 

 have taught only orally. A century elapsed 

 before his doctrines were reduced to writing 

 by Philolaus of Crotona, and it was still 

 later before they Avere taught in public for 

 the first time by Hicetas, or, as he is some- 

 times called, Nicetas, of Syracuse. Then 

 the familiar cry of impiety was raised, and 



