358 Prof. A. Griinwald on the Spectrum of Water-vapour 



2105-9, 2102-2, 2099-6, 2097-5, 2090-8, 2089-7, 2088-2, 

 2087-2, 2085-3, 2078-0, 2038-7, 2034-6, 2033-2, 2031-0. 



The experimental verification of this prediction can only 

 succeed with an altogether special arrangement of apparatus. 

 Possibly the use of several sparks or flames, one behind the 

 other, striking through moist gas (or a broad stream of water- 

 vapour)*, and the observation of the rays emitted in the 

 direction of the line joining them, might succeed, since the 

 rays emitted by the more distant sparks (or flames) would 

 strengthen the vibrations which were produced by those nearer 

 the observing-telescope. It might also be advisable, in accord- 

 ance with a suggestion of my colleague, Prof. Zenger, to 

 bathe the photographic plates in a solution of chlorophyll as 

 concentrated as possible, and then to dry them. 



(2) " The wave-lengths of the elementary line-spectrum of 

 hydrogen may be divided into two groups, (a) and (b) ; so 

 that the wave-lengths of the one group (a) are transformed 

 into corresponding wave-lengths of the water-spectrum by 

 multiplication by the constant 0*6336 (very nearly -^§) 7 and 

 those of the other group (b) by multiplication of the con- 

 stant %." 



From this it follows, by means of theorem I., that hydrogen 

 consists of two primary elements, a and b ; of which the one, 



a, produces the group (a) under the influence of b ; the second, 



b, produces the group (b) under the influence of a. If [a] 

 and \b~\ are relatively the volumes which the substances a and 

 b occupy in a unit-volume of hydrogen, then 



f>] + M=i, 



and, further, 



whence 



[a]: [J] =4:1, [«] = f, [6]=£. 



Hence hydrogen is a compound of one volume of the primary 

 substance b, with four volumes of the other primary sub- 

 stance a: H = ?><2 4 . It is thus a compound analogous to 

 ammonium, NH 4 , of which the volume will increase in the 

 ratio 2 : 3 upon dissociation at a sufficiently high temperature. 

 The substance a is the lightest of all gaseous substances — 

 much lighter than hydrogen ; and the substance b is, if we 

 assume a to be a monovalent element, also a gaseous element 

 and pentavalent similar to nitrogen. The line-spectra of the 



* Or "better, of several such hydrogen flames in oxygen gas. 



