350 



SUMMARY OF CUKllENT RESEARCH ES RELATING TO 



quartz-mercury lamp gives a very quiet and uniform light. An ordinary 

 arc light is more intense in ultra-violet rays, but causes difficulties by 

 reason of the great heat emitted. It is found better to replace the 

 ordinary carbons by Siemens' iron carbons, the effect being to diminish 

 the heat-rays, and therefore to increase the light-energy. Moreover, 

 the lines peculiar to the iron spectrum serve as guides in mapping out 

 results. These iron carbons are carbon impregnated with iron sulphate, 

 and at first throw off numerous particles of incandescent iron whose 

 heat would be detrimental to the filter. After a few moments they 

 subside, however, and the filter should then be inserted. Investigators 

 are warned that the light from the iron carbons is dangerous for un- 

 protected eyes. 



Figs. 65-(;7 show different arrangements of the whole apparatus in 

 a suitable light-proof box B. F is the filter, K the condenser, L the 



?b. 



1 



tO- ftO<A^. 



? 



f"^ 



Fig. 65. 



Fig. 66, 



Fig. 67. 



light-source, L' the image of the light-source, C tbe collector, and C the 

 image of the collector. Fig. 65 is the arrangement for the illumination 

 of a rather large surface. Fig. 6(i represents a powerful effect on a rather 

 small surface, and fig. G7 is an adaptation to small lenses and surfaces. 



The U V-FiUer-lamp is sho^Yn in figs. 68-70. Fig. 6.S shows the 

 arrangement for an optical bench, while in fig. 61) the lamp is fitted to a 

 tripod stand. Fig. 70 is the external view of the complete tripod-lamp. 

 The carbon-holders are governed by rods connected by chain-work with 

 an external milled head on each side of the iron box-case (fig. 70). In 

 order to overcome irregularities in combustion the carbons are inde- 



