482 THE POPULAR SCIENCE MONTHLY, 



spectra may be, they render the spectroscoj^e less trustworthy as a ther- 

 mometric instrument ; for, if the company in which a molecule is placed 

 changes the spectrum in the same way as temperature would, it will be 

 difficult to interpret our results. But, although the discussion of our 

 observations may be rendered more arduous and complicated, we need 

 not on that account despair. It is one of the problems of spectroscopy 

 to find out the composition of bodies, not only qualitatively, but also 

 quantitatively, and, when we shall know in what proportion different 

 bodies are distributed in the sun, we may reduce the problem of find- 

 ing out this temperature to the much simpler one of finding out the 

 temperature of a given electric spark. 



I hope that the few facts which I have been able to bring before 

 you to-night have given you some idea of the important questions 

 which have been brought under the range of spectroscopic research. 

 Many of these questions still await an answer, some have only been 

 brought into the preliminary stage of speculative discussion, but the 

 questions have been raised, and the student of the history of science 

 knows that this is an important step in its development and progress. 

 The spectrum of a molecule is the language which that molecule speaks 

 to us. This language we are endeavoring to understand. The inex- 

 perienced in a new tongue which he is trying to learn does not distin- 

 guish small differences of intonation or expression. The power over 

 these is only gradually and slow^ly acquired. So it is in our science. 

 We have passed by, and no doubt still are passing by, unnoticed dif- 

 ferences which appear slight and unimportant, but which when prop- 

 erly understood will give us more information than the rough and 

 crude distinctions which have struck us at first. We have extended 

 our methods of research ; we have extended our power over the physi- 

 cal agents ; we can work with the temperature of sun and stars almost 

 as we can with those in our laboratories. No one can foretell the 

 result, and perhaps in twenty years time another lecturer will speak 

 to you of a spectroscopy still more modern in which some questions 

 will have received their definite answer, and by which new roads will 

 have been opened to a further extension of science. 



-- 



OPJGIX AND IIISTOEY OF LIFE INSURANCE. 



By THEODORE WEIILE. 



LIFE insurance is based upon the theory that there is a law of 

 mortality governing life ; that is to say, that at all ages from 

 birth to the utmost limits of life a certain proportion of individuals will 

 die during fixed periods. Not that the precise duration of an individ- 

 ual life can be predicted, but that the ratio of deaths out of large aggre- 



