738 THE POPULAR SCIENCE MONTHLY. 



There is, however, one point to which he refers which should not 

 be overlooked. Whatever views we may be disposed to entertain re- 

 specting either the mental conditions in which these phenomena origi- 

 nate, or the external agencies by which these conditions are produced 

 or modified, there is reason to believe that the appearances themselves 

 are really formed upon the retina of the eye, and thus they may be 

 fairly placed in the category of "things actually seen." Science 

 Gossip. 



-- 



COAL AS A EESERYOIR OF POWER. 



By EOBEET HUNT, F. K. S. 



THE sun, according to the philosophy of the day, is the great store- 

 house of Foi'ce. All the grand natural phenomena are directly 

 dependent upon the influence of energies which are poured forth with- 

 out intermission from the central star of our system. Under the in- 

 fluences of light, heat, actinism, and electricity, plants and animals 

 are produced, live, and grow, in all their infinite variety. Those phys- 

 ical powers, or, as they were formerly called, those imponderable ele- 

 ments, have their origin in one or other of those mysterious zones 

 which envelop the orb of day, and become evident to us only when 

 mighty cyclones break them up into dark spots. Is it possible to 

 account for the enormous amount of energy which is constantly being 

 developed in the sun ? This question may be answered by saying 

 that chemical changes of the most intense activity are discovered to 

 be forever progressing, and that to these changes we owe the develop- 

 ment of all the physical powers with which we are acquainted. In 

 our laboratory we establish, by mechanical disturbance, some chemi- 

 cal phenomenon, which becomes evident to our senses by the heat and 

 light which are developed, and we find associated with them the prin- 

 ciple which can set up chemical change and promote electrical mani- 

 festations. We have produced combustion, say, of a metal, or of a 

 metallic compound, and we have a flame of a color which belongs 

 especially to the substance which is being consumed. We examine a 

 ray of the light produced by that flame by passing it through a prism, 

 and this analysis informs us that colored bands, having a fixed angle 

 of refraction, are constant for that especial metal. Beyond this, re- 

 search acquaints us with the fact that, if the ray of light is made to 

 pass through the vapor of the substance which gives color to the 

 flame, the lines of the spectrum which were chromatic become dark 

 and colorless. We trap a ray of sunlight and we refract it by means 

 of a spectroscope an instrument giving results which are already de- 

 scribed in this journal ' when we detect the same lines as those which 



1 Popular Science Review, vol. i., pp. 210-214. 



