4 8 



PRESSURE OF LIGHT 



o 



FIG. 18. 



of glass 1-2 cm. in 

 diameter and O'l mm. 

 thick, with a layer of 

 asphaltum also about 

 O'l mm. thick between. 

 To make a disc the as- 

 phaltum was placed on 

 one plate which was 

 heated till the asphal- 

 tum melted and then 

 the other plate was 

 pressed upon it. The 

 silver surfaces were 

 made by depositing 

 silver from a silver 

 cathode in an ex- 

 hausted receiver on to 

 the outside surface of 

 the disc. 



The discs were then 

 fixed in holes in a 

 plate, fig. 1 8, the 

 centres of the discs 

 being at the corners 

 of a 2 cm. square and 

 the plate was suspend- 

 ed in a flask 16 cm. 

 in diameter by a 

 quartz fibre 9 cm. long, 

 from a spring collar 



