312 Prof. Trowbridge and Mr. Hutchins on 



we have caused the rays from iron vapour to traverse a long 

 and dense layer of iron vapour, and have observed that the 

 strength of the lines and the number of reversals have been 

 largely increased. In another experiment, the lower carbon 

 of the electric lamp we employed occupied the centre of an 

 electro-magnet. This was accomplished by passing the 

 carbon through a hollow iron cone, and surrounding the 

 latter by layers of wire, through which the electric current 

 employed in generating the light passed. In this case the 

 electric arc was spread out at right angles to the pole of the 

 magnet, into a fan-like, intensely hot flame, which roared 

 loudly, and which rarefied, so to speak, the iron vapour 

 between the carbon terminals. The strength of the lines and 

 the number of reversals were diminished under this new 

 condition. 



Another phenomenon may happen. When an excess of 

 the vapour of one metal floats over or is mixed with that of 

 another, the lines of one metal are superimposed upon those 

 of another in the solar spectrum, and the stronger spectrum 

 of one element may easily obliterate the weaker spectrum of 

 another. Thus we have succeeded in completely obliterating 

 the fluted spectrum of carbon in the green and blue, by 

 photographing upon it the spectrum of iron, of nickel, and 

 of cerium. A species of composite photograph v r as thus ob- 

 tained. It is possible that in the future Galton's ingenious 

 method of composite photography may be applied to the solar 

 spectrum ; and by a judicious selection of photographs of the 

 elements, a composite photograph may be obtained which will 

 closely resemble portions of the solar spectrum, and will 

 enable us to judge of the composition of the reversing layers 

 of the sun. 



To the varying conditions which we have thus outlined are 

 due, we believe, the disappearance In the sun's spectrum of 

 the marked fluted spectrum of carbon in the green and blue 

 portions. 



A careful examination of the fluted spectrum of carbon, 

 however, with the juxtaposed solar spectrum, discloses a 

 remarkable fact : while traces of obliteration of the evidence 

 of carbon vapour are seen, yet the general character of the 

 lines in the solar spectrum immediately juxtaposed with the 

 fluted spectrum of carbon near H lead us to believe that 

 there is unmistakable evidence of the existence of carbon 

 vapour in the sun. When the arrangement of the fine lines 

 of the spectrum of carbon is plotted as a curve, and that of 

 the dark lines in the solar spectrum immediately above the 

 carbon spectrum is also plotted, the two curves have a 



