of the Metals. 

 Table III. 



167 







* = 45°. c = 7'-603. 









Transmitted light. 



Reflected light. 



I. 



Po- 



Pl80- 



P- 



8. 



&- 



Ml80* 



P. 



&• 



P- 



8. 



/3- 











r 

 



r 

 



r 

 





45° 54 



45° 42 



45° 4845 10 







O i 



10 













46 4 



46 31 



46 1846 16 









20 



0-098 



0156 



6*1 27 00167 



46 36 



47 26 



47 1 46 39 



0088 



00116 44 18 



30 



0-386 



0-508 



0-447 00588 



48 47 



48 47 



48 47 46 50 



0-756 



0-0994 41 54 



40 



0770 



0-788 



0-779 01024 



50 



50 53 50 26 47 14 



1-764 



232040 29 



50 



1-296 



1-320 



1-308 



01731 



55 6 



54 354 34;48 48 



2-874 



0-378036 9 



60 



1-636 



1984 



1-810 



0-2381 



57 49 



57 3657 4249 59 



4-728 



6218 33 1 



70 



2 324 



2-350 



2-337 



0-3074 



62 44 



61 5 61 5453 57 



7814 



1028 31 17 



80 



3128 



3108 



3-118 



0-4101 



68 39 



67 21 68 59 28 



11-146 1-467 133 23 



85 



3-386 



3-960 



3-673 



0-4832 



71 18 



72 35 71 56 61 32 



13166 1-732 36 34 



Other transparent plates of silver gave similar results, no 

 matter whether their colour in transmitted light was yellow, 

 grey, blue, or violet ; and no matter whether prepared by Petit- 

 jean's method of reduction with tartaric acid, or by Liebig's 

 method of reduction with sugar of milk. The difference of 

 phase is for the same angle of incidence nearly the same, and 

 seems to be independent of the thickness of the film. The 

 azimuth /3, on the contrary, depends upon the thickness and the 

 want of transparency of the silver, being for the same angle of 

 incidence the smaller in proportion as the metallic film is thin- 

 ner and more transparent. On account of the many modifica- 

 tions and conditions in which silver, like other metals, occurs, 

 and which will be again alluded to further on, the author is 

 unable to give any more determinate results, although he has 

 made many measurements. 



The thickness of the plates employed varied from 0*000062 

 millim. to 0*0001827 millim. Thicker plates allowed too little 

 light to pass ; so that it was no longer possible to observe with 

 certainty, especially at the larger angles of incidence, at which 

 indeed the thickness of the silver plate to be traversed by the 

 light was increased. 



Finally the observations made on a platinum film will find a 

 place. This platinum film was obtained by heating the solution 

 of a platinum salt in an ethereal oil (for which the author is in- 

 debted to Professor Bottger) to 600° C. or higher, the solution 

 having been first spread on apiece of plate glass. The platinum 

 was thus obtained in the form of a reflecting film, which had 

 a grey colour and was transparent. The metallic surface was 

 turned towards the heliostat. The reflected light was made to 

 pass through a red glass before reaching the eye, on which 



