[eadie-satterlyJ refractive INDEX OF OXYGEN 



65 



Three copper capillary tubes led from the steel tube, one Fto the oxygen 

 tank, one to a Bourdon pressure gauge G, and the other to the air 

 through a valve V. The pressure gauge read in 251b. steps so that 

 it gave an approximate measure of the pressure but was not fine 

 enough to read small pressure drops. The inlet and outlet capillary 

 tubes were provided with needle valves so that the oxygen could be 

 introduced and released as slowly as desired. 



r/G a. 



The steel tube was placed in one of the interferometer beams. 

 The other beam travelled down through the air alongside the tube. 

 To compensate for the glass ends in the tube two similar glass ends 

 Ci, were placed in the air beam. Also when the oxygen is at high 

 pressure the fringes will not be seen unless compensation is again 

 provided for by inserting glass plates Ci in the air beam. For this 

 purpose different thicknesses of glass were used, microscope cover 

 slips for fine compensation, microscope slide glasses for larger com- 

 pensation, and so on. If many slips of glass are used, there is a great 

 loss of light by reflection and the fringes become very faint and 

 uncountable. The adjustment of the compensating glasses is the 

 chief trouble in the experiment. A variable graduated compensator 

 would be most useful here. However, by repeated experiment and 

 5— c 



