84 Mr Purvis, The influence of very strong 



necessary to analyse it by the calcite to determine if it is merely 

 a widening or if it is a real division. Further, there is obviously 

 a great loss of light when the normal image is divided by the 

 calcite ; and, although some lines are distinctly widened when in 

 the field, they are so much weakened by the calcite dispersion 

 that the images do not appear on the plate even after 1^ hours' 

 exposure. Consequently only the well-marked and the strongest 

 lines were observed. 



To obtain the discharge, an App's coil was used with a large 

 Leyden jar, which could give a spark of 6 inches long. In the 

 case of antimony, bismuth, lead, and tin, it was found necessary 

 not to have such a violent discharge, because the temperature 

 was often raised so high as to melt the ends of the electrodes. 



Maxim's special rapid photographic plates were used and de- 

 veloped with a mixture of metol-hydroquinone. The time of 

 exposure varied from 30 to 90 minutes as required by the nature 

 and intensity of the various lines. 



Results. 



The following notes describe the effect on the various lines 

 whose wave-lengths are mentioned on the left-hand side. 



Gold. 



Wave-length 



X 4792 - 8. A triplet; the two outside members of which seem to 

 vibrate perpendicular to the lines of force between the 

 poles of the magnet, and the inner one parallel thereto. 



4607*8. There seems to be a widening of this line ; but the air lines 

 in the region interfere with a more exact analysis. 



4488-4. This line is distinctly widened; and, on analysing it with 

 the calcite crystal, it seems to be a triplet with the two 

 outer members vibrating perpendicular to the lines of 

 force, and the inner one parallel thereto. 



4437-3. A distinct widening of the line, but it is too weak to 

 affect the sensitive plate when the calcite is interposed 

 to analyse it. 



4315-3. A distinct widening of the line; but it is also too weak 

 as in A 4437-3. 



4065-2, This line is distinctly widened ; and, on analysing it with 

 the calcite, it seems to be divided into a triplet, with 

 the two outside members vibrating perpendicular to the 

 lines of force, and the middle one parallel thereto. 



4053-0. It shows a distinct widening, and when analysed by the 

 calcite, it seems to be a triplet, the two outer members 

 vibrating perpendicular, and the inner one parallel, to 

 the lines of force. 



