﻿certain Gases in Geissler's Tubes. 415 



acid, even if we were to assume that along with the hydrogen 

 some sulphuric-acid vapour had entered the tube. 



Our spectrum cannot be confounded with that of phosphorus 

 or mercury, as follows from Pliicker's descriptions, and as we 

 have convinced ourselves by experiments. Phosphorus exhibits 

 in the green only one group of bright lines, about 8' broad, the 

 most refrangible of which has the minimal deviation of 63° 38'. 

 The mercury-spectrum consists of a series of bands, of which a 

 yellow one is particularly characteristic; moreover, in a tube 

 containing mercury, this spectrum is only formed when the tube 

 is considerably heated. 



To compare the spectrum in question with that of aluminium, 

 wires of this metal were fastened to the ends of the wires leading 

 to the induction-apparatus, and the induction-spark was allowed 

 to strike between these, which were placed in front of the slit of 

 the spectrometer. It was then observed that, according to the 

 distance of the electrodes, the aluminium-vapour might have two 

 essentially different spectra. When the distance of the electrodes 

 was only about two millims., the spectrum consisted of four 

 green splendidly shaded fields. The fields are brightest on the 

 more refrangible side, and gradually diminish towards the less 

 refrangible side ; at distances of 5 minutes these fields are tra- 

 versed by sharp bright lines, and these give quite the appear- 

 ance of fluting to the fields. The right limit of these fields was 

 found, in the minimum deflection, at : — 



1st fluting . . 



. 63° 24 10 



Distance. 



2nd „ . . 



. 64 10 20 



0° 46 10 



3rd „ . . 



. 64 54 40 



44 20 



4th „ . . 



. 65 40 00 



45 20 



The measured distances of the fields (that is, of their right 

 boundaries) are so nearly equal that their differences may be re- 

 garded as errors of observation, since the adjustment is not per- 

 fectly accurate ; the breadth of the fields is about 30' ; so that 

 this spectrum of aluminium consists of four equidistant almost 

 equally broad groups of nutings. 



When the distance of the two wires between which the sparks 

 passed was increased to 10 millims. and more, a totally different 

 spectrum was obtained, both with the use of the small Ruhm- 

 korff and with that of Holtz's machine with superposed con- 

 denser ; the four fluted fields disappeared, and instead of them a 

 number of bright lines and groups of lines started out upon 

 a feebly illuminated background. With the minimum deflec- 

 tion the positions of these lines were : — 



