MODERN SCIENCE. 251 



the absorption of the bright ray (shot from the photosphere) 

 in its passage through the solar atmosphere, by the same 

 kind of substance as that which caused it. If we suppose 

 sodium to exist in the sun, a supposition warranted by the 

 yellow colour found in the continuous and bright line 

 spectra, and look for its intense yellow double line through 

 the spectroscope, we see a dark line at the place it should 

 occupy at the letter D of Fraunhofer's map of dark lines. 

 And knowing that the dark line D can be produced only 

 by the absorption of the sodium ray by the sodium vapour, 

 it is inferred that the sodium light is shot from a centre 

 the photosphere and is arrested or absorbed in its 

 course by an atmosphere of incandescent metallic vapours 

 in which sodium gas is also present. Hence two facts are 

 ascertained, viz., that the sun itself is a luminous body 

 made up of certain substances, and that it is surrounded 

 by an atmosphere composed of (cooler) gases mostly of the 

 same substances, for what is true of sodium is true of other 

 elements. Aluminium, barium, cadmium, calcium, carbon, 

 cerium, chromium, cobalt, copper, hydrogen, iron, lead, 

 magnesium, nickel, potassium, rubidium, strontium, uranium, 

 zinc, etc., are known to be present in the sun, because 

 their lines are suppressed by the solar atmosphere. So far 

 as we know, thirty-six of our terrestrial elements exist in 

 the sun, eight are doubtful, fifteen have not been found 

 yet in the solar spectrum. Likewise, stars seem to be 

 constituted like our sun, and to consist of a nucleus and 

 an atmosphere composed of some of the elements existing 

 in our globe. Meteorites are also composed of some of 

 our elements, iron particularly. Comets differ little from 

 meteorites, if at all. Nebulae exhibiting no dark lines can 

 be gaseous bodies only, so far as we are aware at present. 

 All these facts have become known to us by the use of 

 the spectroscope, one of our most admirable agents. The 

 services this instrument has rendered science by far surpass 

 in number and importance those done by any other, the 

 telescope and microscope not excepted. It led at once 

 Bunsen and Kirchhoff to the discovery of two new metals, 

 CESIUM and RUBIDIUM. It has enabled astronomers to 



