908 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



acid. This mixture has the eflect of removing all traces of hypo- 

 sulphite without generating any deleterious compound or disen- 

 jrairinor free chlorine sr^is, which Avould attack the raetalic silver iu 



Geo C ' 



the pictures. 



SPECTltUlM OF THE VArOR OF TVaTER. 



Mr. Jangsen, under the patronage of the Minister of Public 

 instruction of France, has, by a series of experiments, proved 

 that certain lines in the solar spectrum of variable intensity, iirst 

 discovered by Sir Edward Brewster, and termed by him telluric 

 rays, are not caused b}' water in solution in the atmosphere, but 

 are the direct effect of water vapor, as had been previously con- 

 jectured by Father Secchi. When light is passed through a tube 

 filled with vapor, under the pressure of seven atmospheres, it 

 shows the principal telluric rays. Janssen dissents from the con- 

 clusions of Kerchoff, who attri])utes a portion of the lines in ques- 

 tion to potassium. The red and yellow being found more bril- 

 liant than the blue and violet in the spectrum of water-vapor, the 

 color of the vapor should be orange; this also accounts for the 

 red of the rising and setting sun, or the sun wheu seen near the 

 horizon. 



A Normal Map of the Solar Spectrl^i. 



Prof. Walcott Gibbs, of Harvard University, in a memoir read 

 before the National Academy of Sciences, described his Normal 

 Map of the Solar Spectrum, in which each spectral line is entered 

 according to its wave length, as first suggested by Billet. The 

 well known chart of Kirchhoff", though executed with great care 

 and labor, is not, properly speaking, normal, since it only repre- 

 sents a spectrum formed by four fiint glass prisms, the angles of 

 which, it is true, are given, but of which the indices of refraction 

 are not stated. Moreover, the prisms were not placed accurately 

 in the positions of least deviation, for each of the spectral lines. 

 Prof. Gibbs obviates these objections b}'' making a standard map 

 wholly independent of the peculiarities in the form of apparatus, 

 in the number oi prisms, their refractive and dispersive powere, 

 and their positions. His map is based on the wave lengths of 

 spectral lines, which do not vary witli the material of Avhich the 

 prism is composed. Angstrom's measurements were selected as 

 standards; these being in ten-millionths of a Paris inch, have been 

 reduced by Prof. Gibbs to millionths of a millimeter. A new 

 method of determining wave lengths by comparison was described 



