PRESSURE EFFECT UPON ABSORPTION. 559 



pure rubber tubing, filled the space between the glass and the steel. 

 The washer was wrapped with fine thread after it was put on the win- 

 dows in order to make it possible to insert the window and the washer 

 into the opening. The thread breaks upon tightening the packing 

 when the plug is screwed in at P. A thin fibre washer, F, placed at the 

 end of the steel bearing, H, served as a guide for the window. A piece 

 of thin paper was placed between the end of the window and the steel 

 bearing, K, which was held in place by the plug screwed in at P. A 

 hole T6 of an inch in diameter through the center of the bearing and 

 the plug allowed for the transmission of light. 



Pressure was supplied by a hand pump of 1000 kg per sq. cm. 

 capacity connected to an intensifier having a piston ratio of 4 to 1. 

 The intensifier served to separate the pump liquid from the clear oil in 

 the optical parts. A manganin pressure gauge was inseited between 

 the intensifier and the plug at the top of O, Figure 1, through which 

 connection was made with the observation chamber. 



Procedure. 



The observation chamber, O, Figure 1, was filled with neutral white 

 oil, the medium used for the transmission of pressure, and air bubbles 

 were removed by means of a vacuum pump. A steel container holding 

 the mounted specimen was lowered into position S, and the plug 

 through which connection was made to the intensifier was screwed 

 into the top of O. The source of light, A, the lens, L, and the colli- 

 mator of the spectroscope, C, were then placed accurately in line with 

 the windows, G G and the specimen, S. 



The spectrum of the light transmitted through the specimen was 

 photographed, first, at normal pressure, then, after the pressure was 

 raised. By use of a divided slit, the two exposures were made adja- 

 cent to each other and the comparison spectrum was photographed on 

 the edge of each without any change in the adjustment of the ap- 

 paratus. For most of the work Wratten and Wainwright panchro- 

 matic plates were used but for the study of absorption bands of greater 

 wave-length than 7000 Angstrom units, Seeds 26 plates dyed with 

 Eastman red-sensitive dye were prepared. Simultaneously with the 

 taking of the picture of the absorption spectrum, the corresponding 

 pressure was determined by measuring the change in resistance of the 

 manganin gauge. 



