478 THE POPULAR SCIENCE MONTHLY, 



solvent has as mucli to do with the amount of shifting observed as 

 the molecular weight or the dispersion or refractive power may have. 

 The shifting of the absorption bands in different solutions of the same 

 substances is only one of many applications of spectroscopes to the 

 examination of molecular phenomena in liquids. Into the interesting 

 researches of Professor Russell, who has greatly extended this field of 

 inquiry, we have no time to enter. 



The changes of spectra due to molecular combinations and rear- 

 rangements have in addition to their theoretical importance a great 

 practical interest, for they will afford us some day a means of answer- 

 ing approximately a great many questions relating to the temperature 

 of sun and stars. The gases and vaj^ors in the solar atmosphere are 

 for the greater part in the molecular condition in which they give a 

 line-spectrum, and we know of stars the spectra of which resemble our 

 solar spectrum very nearly. We shall not be far wrong in ascribing 

 to such stars a temperature similar to that of our sun. Other stars 

 have absorbing envelopes showing spectra of fluted bands. We know 

 that fluted bands belong to a more complex molecular condition, which 

 only can exist at lower temperatures. These stars, therefore, must 

 have a lower temperature than our sun. Dr. Huggins, who has suc- 

 ceeded in obtaining most valuable photographs of star-spectra, has 

 been able to classify and arrange star-spectra ; and it is more than 

 likely that, in the series of stars arranged in order by means of their 

 spectra, we have at one end those of the highest, at th other those of 

 the lowest, temperature. We are as yet far from being able to assign 

 any particular temperature to a star, but the question by means of the 

 spectroscope has been reduced to one which can be decided in our 

 laboratories, and, however difficult it may be, we may rest assured that 

 it will ultimately be solved. As to our sun, its temperature has been 

 the subject of many investigations. Attempts have been made to 

 deduce it (at least approximately) from the amount of heat it sends 

 out. Different experimental laws have been proposed to connect to- 

 gether the heat radiation of a body, and the temperature of that body. 

 The first law which was thus proposed gives 10,000,000 Centigrade 

 as a lower limit ; the second law reduces that lower limit to a little 

 over 1,500. Both these laws we now know to be wrong. More ac- 

 curate laws give something like 10,000 or 20,000, but the whole 

 method employed is one which is open to a greafr many objections. 



We measure the combined heat radiation of different layers on the 

 solar surfaces, all of which are at different temperatures, and we ob; 

 serve only an average effect which is much influenced by the absorp- 

 tion in the outer layers of the solar atmosphere and in the corona, and 

 does not admit of easy interpretation. The spectroscopic method, 

 which is yet in its infancy, has the advantage that we can observe 

 separately each layer of the sun ; and we thus examine the tempei'a- 

 ture not as an average, but for every part of the solar body. Our way 



