8o THE POPULAR SCIENCE MONTHLY. 



which were reversed in the atmosphere of the sun. Hence, when we 

 observe a single coincidence between a dark solar line and the bright 

 line oi" any metal, we are further led to inquire whether this bright 

 line is one of the long lines which will continue to exist all the way 

 between two terminals of that metal when the spark passes. 



If this be the case, then we may argue with much probability that 

 the metal in question really occurs in the solar atmosphere ; but if, on 

 the other hand, the coincidence is merely between a solar dark line 

 and a short bright one, then we are led to imagine that it is not a true 

 coincidence, but something which will probably disappear on further 

 examination. This method has already aftbrded us a means of deter- 

 mining the relative amount of the various metallic vapors in the sun's 

 atmosphere. Thus, in some instances all lines are reversed, whereas 

 in others the reversal extends only to a few of the longer lines. 



Several new metals have thus been added to the list of those pre- 

 viously detected in the solar atmosphere, and it is now certain that 

 the vapors of hydrogen, potassium, sodium, rubidium, barium, stron- 

 tium, calcium, magnesium, aluminium, iron, manganese, chromium, 

 cobalt, nickel, titanium, lead, copper, cadmium, zinc, uranium, cerium, 

 vanadium, and palladium, occur in our luminary. 



I have spoken hitherto only of telescopic spectroscopy ; but pho- 

 tography has been found capable of performing the same good service 

 toward the compound instrument consisting of the telescope and its 

 attached spectroscope, which it had previously been known to perform 

 toward the telescope alone. It is of no less importance to secure a 

 permanent record of spectral peculiarities than it is to secure a perma- 

 nent record of telescopic appearances. This application of photogra- 

 phy to spectrum observations was first commenced on a sufficient scale 

 by Mr. Rutherford, of New York, and already promises to be one of 

 the most valuable aids in solar inquiry. 



In connection with the spectroscope I ought here to mention the 

 names of Respighi and Secchi, who have dotie much in the examina- 

 tion of the solar surface from day to day. It is of great importance 

 to the advancement of our knowledge, that two such competent ob- 

 servers are stationed in a country where the climate is so favorable to 

 continued observation. 



The examination of the sun's surface by the spectroscope suggests 

 many interesting questions connected with other branches of science. 

 One of these has already been alluded to. I may mention two others 

 put by Mr, Lockyer, premising, however, that at present we are hardly 

 in a position to reply to them. It has been asked whether the very 

 high temperatures of the sun and of some of the stars may not be suffi- 

 cient to produce the disassociation of those molecular structures which 

 cannot be disassociated by any terrestrial means ; in other words, the 

 question has been raised, whether our so-called elements are really 

 elementary bodies. 



