284 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Dec, 1904. 



paper in which the photographic plate had been 

 wrapped. Another piece of perforated zinc served as 

 the obstacle. It can be faintly .seen with the shadow- of 

 the iron support running across it almost parallel to 

 the edge of the print. 



We next tried the effect of rapidly evaporating some 

 ether in our apparatus. We used a piece of bromide 



Fig. 5- Oct. 8=10.1004. 2 days. Calcium Carbide and Water. 

 Obstacles : Zinc tone piece plain, one perforated). 



paper, carefully protected* from actual contact with 

 the vapour, and placing a penny as the obstacle, we 

 endeavoured to obtain an " instantaneous " photo- 

 graph by a three-hours' exposure. 



Fig. 7 shows most clearly the effect of a chemical 

 reaction. Here the piece of perforated zinc can be 



Fig. 6.— Oct. 4, 1904. Exposed for three hours to ether vapour. 

 Obstacle : Penny. 



plainly distinguished ihrougli the iron arm of the sup- 

 port. The obstacle on the right is a plain piece of zinc. 

 The plate is the result of the slow decomposition of 

 hydrogen peroxide, H.jO., — Il,(_) 4- O, lasting over 

 a period of thirteen days. 



Our last effort was to expose a plate to some euca- 

 lyptus oil for a period of thirteen days. 



We are not aware that any chemical change goes 

 on when this oil is left alone, nor could it have evapor- 



Fig. 7.-0ct. 8.21, 1904. 13 days. HoOj. 



atcd to any extent, seeing that the box was closed the 

 whole time; vet the plate shows some action of some 



* Ether blackens bromide paper on development. 



Oct. N = 2i, 1904. 13 dayj. l;iEcaljptus oil. 



kind, and we leave it to the efforts of the readers of 

 " Knowledge " to suggest a satisfactory explanation. 



Note. — Will Mr. A. F. Burgess communicate his address to 

 the Editor. 



Spectrum Analysis. — It is not quite easy to classify "-An In- 

 troduction to Spectrum Analysis" (Longmans. Green), by Dr. 

 Marshall Watts, which is something between a textbook and a 

 work of reference. Perhaps its best title is the one that has 

 been found for it ; and it may be confidently recommended to 

 students who wish to take up the study of spectroscopic 

 methods from the beginning. It is divided into two portions ; 

 the first of which describes spectroscopic work and discusses 

 the uses of instruments ; the Fraunhofer lines of the solar spec- 

 trum, the meanings and implications of the " Zeeman Effect," 

 and of obser\ations in stellar spectroscopy generally ; the 

 Michelson echelon diffraction grating; and the work of Pro- 

 fessor Hale with the spectro-heliograph. The second part of 

 the book embraces some hundred and eighty pages of cata- 

 logue of spectra. 



