1889.] on Optical Properties of Oxygen and Ozone. 473 



and somewhat expanded. The diffuse edges of several bands now 

 extende Ifrom about — ( I) X 6410 to 6190, (2) A 5865 to 5635, (3) X 5350 

 to 5280, (4) A 4820 to 4710, A 4480 to 4455. 



Photographs taken when the pressure of the oxygen was 90 atmo- 

 spheres show a faiut absorption-band about L of the solar spectrum, 

 a stronger band extending from about A 3600 to 3640, a broad diffuse 

 band about the place of the solar line 0, and complete absorption 

 abova P. The accompanyini^ diagram, Fig. 3, represents the ab- 

 sorption of 18 metres of ordinary oxygen at a pressure of about 97 

 atmospheres. 



The absorbent column in the tube at the highest pressure used con- 

 tained a mass of oxygen about equal to that in a vertical column of the 

 earth's atmosphere of the same section as the tube ; but the intensity 

 of the bands produced by the compressed gas was far greater than that 

 of the corresponding bands in the solar spectrum with a low sun. 

 When the arc light was replaced by a piece of white paper reflecting 

 light from the sky through the tube, it appeared to the naked eye to 

 have a faint blue tint, similar to that of liquid oxygen, which, com- 

 paring our observation with Olszewski's, seems to have the same 

 absorptive powers as the dense gas, if we except A. This exception 

 is probably only apparent, and due to the difficulty of observing A 

 under the circumstances of Olszewski's experiment. 



The greatly increased intensity of the absorption-bands at high 

 pressures bears out Jansen's observation, that in this group the 

 absorption is proportional to the product of the thickness of the 

 absorbent stratum into the square of its density, while the absorptions 

 to which A and B belong vary directly as the density. 



The appearance, on looking through the tube when gas at high 

 pressure is streaming into it, is very much like that of a black and 

 a colourless liquid, which do not mix, being stirred together, and the 

 tube soon ceases to transmit any light. Transparency returns as the 

 dens'ty becomes uniform. Currents produced by heating the tube at 

 one or two points produce a similar effect, and show that such currents 

 in the atmosphere of a star may stoj) all rays coming from its 

 interior. 



We hope bef )re long to get the tube fitted with rock-salt ends 

 and lenses, and to determine the total absorption of radiation by 

 similar masses of oxygen, nitrogen, and hydrogen. 



[J. D] 



