Intelligence and Miscellaneous Articles, 393 



order to cut out all of the more refrangible part of the underlying 

 spectrum. In some cases a weak solution of iodine in carbon 

 disulphide was used with good effect. 



Xo difficulty was found in photographing from the A line to 

 wave-length 9900, or to the limit assigned by Abney as the limit 

 of the diffraction spectrum. Xone of the lines were reversed. A 

 special study of the A group was made, photographs being taken 

 at different seasons, in order to see if any changes in the remark- 

 able group of lines constituting the A group could be noticed. No 

 existing map represents this group correctly. Employing the 

 second spectrum produced by a concave grating, 52 lines were 

 observed between wave-lengths 7100 and 8000. In the same 

 space Abney records only 24 lines. Between the head of A and 

 the tail of A, the latter being the single line before the series of 

 doublets begin which is so characteristic of the A group, my pho- 

 tographs show 17 lines. These photographs were taken in June 

 between ten and one o'clock. 



These results are of special interest when we consider that 

 Abney has said in a Bakerian lecture, "As a result of these 

 experiments I can confidently state that in no case did the addition 

 of a dye cause any chemical effect to be produced by the rays 

 below A of the solar spectrum, nor has Vogel claimed that they do." 



It is interesting to note that Abney is led to believe that the 

 photographic action, which has been noticed hitherto, by the use of 

 dyes as sensitizers, can be attributed to a certain action of nitrate 

 of silver on organic matter. This effect is a bleaching one, and 

 only the more fugitive dyes can produce it. We are led to con- 

 clude from Abney's paper, that be believes that only a chemical 

 effect produced in a specially prepared emulsion can be used to re- 

 produce the infra-red rays. After many experiments he succeeded 

 in producing such an emulsion. The colour of this verged upon 

 the blue. Since the colour of plates stained with cyanine by the 

 process I have described is also blue, there may be some physical 

 significance in this resemblance. 



My experiments show that a specially prepared emulsion is not 

 necessary for the photography of the infra-red region. The 

 chemical theory advanced by Abney, therefore, seems to need 

 revision. 



ON THE DISINTEGRATION OF IGNITED FLATINUM. 

 BY H. KAYSER. 



Attention has recently been again directed from various quarters 

 to the phenomenon that ignited platinum throws off minute par- 

 ticles, and thus disengages dust, and this irrespective of how the 

 ignition is produced, whether by the electrical current or by a 

 flame. I wish to communicate a case of this kind, which has 

 resulted in an important condition for the air-thermometer. 



In the year 1885 I was engaged in determining the coefficient 

 of expansion of air with the utmost accuracy, namely as a function 



Phil. Mag. 8. 5. Vol. 26. No. 161. Oct. 1888. 2 D 



