CHEMISTRY. 



131 



part of tho sun examined, bat we know thin 

 because we see the bright lines, not (as usual) 

 the dark lines of that element. 



If oxygen were present in very great quanti- 

 ties in the sun, but always lay below the visi- 

 ble solar surface, and were at a higher tempera- 

 ture than that prevailing at the surface, then 

 oxygen might indicate its presence by its 

 bright lines, and could certainly indicate it in 

 no other way. Now, it is evidence of precisely 

 this kind that Professor Draper seems to have 

 obtained respecting this most important ele- 

 ment. He had been engaged since 1863 in 

 obtaining simultaneous photographs of parts 

 of the solar spectrum and of corresponding 

 parts of the spectra of hydrogen, nitrogen, and 

 carbon. In examining a series of such photo- 

 graphs in which the fluted spectrum of nitrogen 

 was in juxtaposition with the solar spectrum, 

 he found reason to suspect that some of the 

 bright lines of nitrogen agreed exactly in posi- 

 tion with bright bands in the spectrum of the 

 sun. Pursuing his researches, he found, even 

 at that early stage of his labors, very striking 

 evidence of agreement between the bright 

 lines of oxygen and solar bright bands. It was 

 not, however, till the year 1877 that he was so 

 far satisfied as to announce "the discovery of 

 oxygen in the sun." The paper thus named 

 was illustrated by enlarged views of the nega- 

 tives he had obtained. In these photographs 

 a part of the spectrum of the sun was seen side 

 by side with the bright-line spectrum of air. 

 The bright lines of iron were shown in com- 

 pany with those of air, in order to indicate the 

 exact agreement of the juxtaposed spectra by 

 the coincidence of the iron bright lines with 

 the corresponding solar dark lines. Every one 

 of the oxygen bright lines was seen to coin- 

 cide with a bright part of the solar spectrum. 

 In some cases the coincidence was very strik- 

 ing, because the bright line of the air-spectrum 

 not only agreed exactly in position, but very 

 closely in character also, with a bright band in 

 the solar spectrum. This close resemblance 

 could not in every case be recognized a cir- 

 cumstance by no means surprising when wo 

 remember that if these bright bands in the 

 solar spectrum are really due to the presence 

 of great quantities of oxygen below the visible 

 solar surface, the light of this oxygen can only 

 reach us after passing through the cooler en- 

 velope of metallic vapors which produces the 

 dark lines, and must be affected by tho absorp- 

 tive action of those vapors ; which, of course, 

 was not the case with the oxygen of the air 

 from which Professor Draper obtained tho 

 bright-line comparison spectrum. 



Many experienced spectroscopists remained 

 unconvinced by the evidence which Professor 

 Draper thus advanced in 1877; and in the true 

 scientific spirit Professor Draper set to work to 

 apply more searching tests to his result. The 

 scale of his enlarged photographs had been 

 half that of Angstrom's well-known "normal 

 spectrum." Those which he exhibited at the 



Astronomical Society were on a scale four 

 times greater. The evidence derived from 

 each coincidence was thus increased fourfold in 

 value, tho evidence from two coincidences six- 

 teenfold ; from three, sixty-fourfold ; and from 

 the eighteen recognized coincidences about 

 68,726,000,000 times. lie effected also an im- 

 provement likely to have great value in other 

 spectroscopic researches. The electric spark 

 through air which gave the air-spectrum pur- 

 sued a zigzag course, like a lightning-flash on a 

 small scale. He wanted a straight flash, or at 

 any rate a flat flash, so that seen from one 

 direction it should appear as a straight line. 

 So he invented what he calls the spark-com- 

 pressor. The terminals between which the 

 spark passes are introduced into a small block 

 of soapstone, and between them a small flat 

 aperture is prepared, between the walls of 

 which the electric flash has to travel. This 

 space is left open on one side, somewhat like 

 the slit of a money-box, and the spark seen 

 from that side necessarily appears as a straight 

 line, though it may have a considerable amount 

 of zigzag play in the plane of the flat space 

 left for its passage. The result of this arrange- 

 ment is that the spectrum of the air-lines (oxy- 

 gen and nitrogen), as also of the iron -lines 

 (obtained by having a little iron at one of the 

 poles), is much better defined and more trust- 

 worthy than it had been before this plan was 

 adopted. 



Most spectroscopists will doubtless admit 

 that Professor Draper does not pass beyond 

 the limits of scientific caution in claiming that 

 the coincidence, shown in his photographs, be- 

 tween the bright lines of oxygen and bright 

 parts of the solar spectrum, establishes the 

 probability of the existence of oxygen in the 

 sun. The burden of proof, or rather of dis- 

 proof, should now fall on those who consider 

 that the coincidence may, after all, be merely 

 accidental. If such evidence as Professor Dra- 

 per has obtained is rejected, it would seem as 

 if hardly any spectroscopic evidence can suffice 

 to prove the existence of an element in the 

 sun. The evidence is certainly not stronger 

 in the case of sodium or magnesium, which 

 every physicist regards as present in the sun, 

 than Professor Draper has obtained in the case 

 of oxygen. 



A New Explosive. The discovery of a com- 

 pound more violent than guncotton or dyna- 

 mite has recently been announced by M. Nobel 

 under the name of blasting gelatine, and this 

 again has been endowed with a still greater 

 energy by a modification of its nature effected 

 by Professor Abel, chemist of the British War 

 Department. Nearly all the explosives brought 

 before the public are nitro-compounds or mod- 

 ifications of them. One class owe their origin 

 to guncotton and the other to nitro-glycerine ; 

 and these are essentially the same thing, gun- 

 cotton being made by the nitrification of a 

 solid body, and nitro-glycerine by the nitrifi- 

 cation of a liquid substance. The methods ol 



