132 



THE POPULAR SCIENCE MONTHLY. 



of the spectroscope. Up to 1866 it had 

 been possible to examine the solar promi- 

 nences only during eclipses. In that year 

 Mr. Lockyer devised a method of observa- 

 tion which can be used at other times, mak- 

 ing for the observer what have been called 

 " artificial eclipses." It was the illumination 

 of our air that interfered with such obser- 

 vations, and he abolished this interference 

 by using several prisms in the spectroscope, 

 which, by successive dispersions, so greatly 

 enfeebled the continuous spectrum of the 

 light diffused in the air, that the bright 

 lines due to the prominences could be read- 

 ily seen. Current investigations were being 

 made on the basis of Kirchhoff's hypothe- 

 ses, that the absorption which produced the 

 Fraunhofer lines took place at some dis- 

 tance above the photosphere, the spots be- 

 ing solar clouds, and that the chemical ele- 

 ments present in the solar atmosphere were 

 identical with some of those existing on the 

 earth, and their spectra were identical. The 

 observations of Mr. Lockyer and his collabo- 

 rator, Dr. Frankland, soon led them to pro- 

 pose modifications in Kirchhoff's theory, for 

 they showed that the dark lines increased 

 both in width and number as the photo- 

 sphere was approached. Moreover, the lines 

 in the spectra of the various terrestrial ele- 

 ments were found not to coincide so per- 

 fectly with the Fraunhofer lines as had 

 been believed. Certain lines were found in 

 the spectra of two or more substances, and 

 the same substance was found to have more 

 than one spectrum. Difficulties multiplied. 

 The sun had been regarded as a type of 

 what our earth once was, but spectrum 

 analysis apparently showed it to have a 

 chemical constitution widely different from 

 that of the earth's crust. Only one terres- 

 trial substance classed as non-metallic (hy- 

 drogen) had been found on the sun, while 

 no trace of elements so common on the 

 earth as oxygen, silicon, and chlorine, could 

 be discovered. It had been noted by Ang- 

 strom that spectral lines vary their intensi- 

 ties with the temperature. This is the start- 

 ing-point from which Mr. Lockyer develops 

 his theory of the chemical constitution of 

 the solar atmosphere. When a metallic com- 

 pound vapor is dissociated by the electric 

 spark, the character of its spectrum changes 

 from channeled and banded to lined. The 



effect of increasing degrees of heat within 

 the limits known on the earth is to reduce 

 compound bodies to simple ones. Now, on 

 the sun occur temperatures immeasurably 

 greater than we are able to produce on the 

 earth, and it occurred to Mr. Lockyer to 

 ask if iron, for example, were subjected to 

 the heat of the sun, whether it would ex- 

 hibit the spectrum of iron, or the spectra 

 of some simpler substances the constitu- 

 ents of iron. Many facts relating to ter- 

 restrial, solar, and stellar spectra unite to 

 convince him that in the reversing layer 

 of the sun a high degree of celestial dis- 

 sociation is at work, which prevents the 

 coming together of the atoms which at all 

 temperatures yet attained on earth compose 

 the metals, metalloids, and compounds. He 

 has applied many and various tests to this 

 theory, but the results of all serve only to 

 confirm his belief. The theory also seems 

 to him to conform satisfactorily to the 

 observed physical phenomena of the sun. 

 Mr. Lockyer has stated his views, and 

 detailed the investigations which led up 

 to them, in a way that will command the 

 attention and respect of scientists, even 

 where he does not produce conviction. 

 Moreover, his work and that of his prede- 

 cessors has been described in so clear and 

 interesting a style, that the general reader 

 will be able to go through the book with 

 pleasure and profit. 



Mineral Piitsiology and Physiography. 

 A Second Series of Chemical and Geo- 

 logical Essays, with a General Introduc- 

 tion. By Thomas Sterry Bunt, M. A., 

 LL. D. (Cantab ). Boston : Samuel E. 

 Cassino. Pp. 710. 



The essays of which this volume is made 

 up have been written in accordance with 

 a predetermined plan that is now accom- 

 plished. The first and second are intended 

 to serve as a general introduction, and to 

 show the relations of the natural sciences to 

 each other, and to that complex study known 

 as geology. 



The first essay is entitled "Nature in 

 Thought and Language," and gives histori- 

 cal and philosophical reasons for the use 

 of the term physiology in relation to the 

 mineral kingdom. The second embodies a 

 simple scheme for the classification of the 

 natural sciences, by which the sciences of 



