Intelligence and Miscellaneous Articles. 469 



Time of irradiation .... 2 5 10 15 20 seconds. 

 Deflection 270 300 321 328 331 



Absorption of Radiant Heat in Glass. 



The absorption of the rays which proceeded from an ignited 

 platinum foil was first examined in various kinds of glass. The 

 platinum foil was in the non-luminous flame of a Bunsen's burner. 

 The glass plates were chosen from pieces of window-glass and of 

 plates of electrical machines, and had approximately the same 

 thickness, for only in this case can the absorptions of the various 

 plates be compared with each other. 



The coefficient of absorption was calculated from the formula 



j=j>-h 



to Jc = 



Jo 



J, 



00 



in which 



oo is the thickness of the absorbing plate, 



J the intensity of the incident, 



J that of the transmitted rays. 



The following table gives a representation of the absorption in 

 the disks chosen : — 



Thickness of 

 the disks. ' 



Jo- 



J. 



k. 



milliiii. 

 1-8 



142-9 



700 



0-396 



1-8 



143-0 



69-5 



0-400 



1-75 



142-5 



70-5 



0-401 



1-70 



142-5 



71-5 



0-405 



1-90 



142-0 



68-5 



0-383 



The table shows that the glass plates investigated possess a 

 pretty equal absorptive power ; the larger variations which occur 

 with No. 4 and No. 5 are easily explained from the different thick- 

 ness of the two plates. It results from the following that the 

 coefficient of absorption greatly decreases with increased thick- 

 ness. 



The question was further investigated, How is the coefficient of 

 absorption altered at various depths of the irradiated layer of 

 glass ? The following table elucidates this : o is the thickness of 

 the glass plate already traversed before the absorption in the glass 

 plate of 1*75 millim. thickness is measured. A luminous gas- 

 flame served as a radiating source. 



