560 



SUMMABY OF CURRENT RESEARCHES RELATING TO 



^ The improved apparatus is shown in Fig. 105. It is made by M. 

 Verick, and consists of a thick brass slide, having in the centre an 



Fig. 105. 



Fig. 106. 



aperture, into which is fixed a circular glass block about a centimetre 

 in diameter, with its upper surface level with the top of the slide, and 



