504' Prof. K. Warlmann on some Nexv Lines 



tion of the spectrum was 0™-lG in length and 0™'055 in height. 

 I ought also to notice that the flat sides of the bottle were five 

 millim. thick, and at 0™'04-3 distant from each other. I in- 

 troduced into it some crystals of iodine, which I caused to 

 pass slowly into the state of vapour. The bottle was placed on 

 some sand, and it was heated by means of some incandescent 

 charcoal placed on the sheet of iron, which sustained it as well 

 as the sand. As soon as the vaporization of the iodine had 

 begun, some excessively thin and ill-defined lines appeared in 

 the field of the spectrum. By increasing the quantity of 

 vapour, this spectrum appeared covered with thousands of 

 longitudinal, exceedingly fine black lines; by degrees they 

 united in a system of large and small, accompanied by some 

 which were luminous, and at last they divided into two ex- 

 cessively black systems, one superior, the other inferior, se- 

 parated by a zone of intense light five millim. in width. After 

 the fire had been removed, the vapour of iodine returned by 

 degrees to the solid state, and the two black systems weresubdi- 

 vided as well as the luminous band. I have observed perfectly 

 similar phaenomena with nitrous gas. It is wonderful to see 

 some thousands of longitudinal lines in constant motion, owing 

 to variations of temperature*. ... I have thus convinced my- 

 self of the existence of the two following facts : — 1, the internal 

 motion of the vapours, as well as that of the translation of the 

 vessel, produce an indescribable variety in the distribution of 

 the black and luminous lines : 2, rarefaction of the gases causes 

 a subdivision of the black lines, condensation unites or in- 

 creases these lines. All this is in perfect harmony with the 

 variations produced by the atmosphere. When a subtle veil 

 of vapour suspended in the upper regions merely softens the 

 intensity of the azure of our sky, the spectrum presents some 

 excessively fine longitudinal lines in its field, so fine that the 

 eye, not aware of their existence, is unable to perceive them. 

 The lines marked q in my figure have several times presented 

 the phoenomenon of their separation and reunion, accompanied 

 by the successive appearance or disappearance of an interposed 

 luminous line. These variations were observed for more than 

 ten days, during which the state of the atmosphere constantly 

 varied ; and I have also always detected changes in the focal 

 distance-)-." 



• The author does not appear to have paid any attention to the move- 

 ments of the heated air around his prism. 



t Those who may consult the work from which we have translated the 

 preceding lines, will perhaps not consider as out of place some critical notes 

 on the chapter which now occupies us. In the first place, the simplified 

 method employed by the author in order to project his lines upon a screen, 

 is due to M. de Haldat, who described it as early as 1838 in the Mimoires 



