1889.] on Optical Properties of Oxygen and Ozone, 4G9 



placed about 10 centimetres from one end of the tube, an image 

 of it was formed on the slit of the spectroscope at about the same 

 distance from the other end of the tube, and thereby loss of light, 

 so far as it was due to the distance of the source, was reduced to a 

 minimum. 



Ordinary oxygen was let into the tube from an iron bottle until 

 the pressure reached 85 atmos2>heres, and on viewing an arc light 

 through the tube the following absorptions were visible : — 



(1) A very dark band sharply defined on its more refrangible 

 side, gradually fading out on its less refrangible side, and divided 

 into two parts by a streak of light, occupying the jjosition of A of 

 the solar spectrum. 



(2) A much weaker, but precisely similar band in the position of 

 B of the solar spectrum. 



(3) A dark band very diffuse on both edges, extending from 

 about X 6360 to X 6225, with a maximum intensity at about A. 6305. 



(4) A still darker band a little above D. beginning with a diffuse 

 edge at about A. 5810, rapidly coming to a maximum intensity at 

 about A. 5785, and then gradually fading on the more refrangible 

 side, and disappearing at about X 5675. 



(5) A faint narrow band in the green at about A. 5350. 



(6) A strong band in the blue, diffuse on both sides, extending 

 from about X 4795 to A 4750. 



When photographs were taken of the ultra-violet part of the 

 sj^ectrum of the arc and of the iron spark, the gas appeared to be 

 quite transparent for violet and ultra-violet rays up to about X 2745. 



From that point the light gradually diminished, and beyond 

 X 2664 appeared to be wholly absorbed. 



The pressure of the oxygen in the tube was then increased to 140 

 atmospheres. This had the effect of increasing sensibly the darkness 

 of all the bands above described ; but brought out no new bands, 

 excej)t a faint band in the indigo at about X 4470. In the ultra- 

 violet the absorption appeared to be complete for all rays beyond 

 about X 2704. 



The foregoing observations were made with a spectroscope of 

 small dispersion. We next brought to bear on the spectrum a large 

 instrument with one of Eowland's gratings. Even with the high 

 dispersion of this instrument, the bands at A could not be resolved 

 into lines; they remained two diffuse bands; though the red 

 potassium-lines, which were produced by sprinkling the electrode of 

 the arc with a potassium-salt, were sharply defined and widely 

 separated. None of the other bands were resolvable into lines. This 

 we attribute to the density of the gas, by which the lines are expanded 

 so as to obliterate the interspaces ; and this supposition is confirmed 

 by the observation of Angstrom, that the band in the solar spectrum 

 which appears to be identical with that observed by us a little above 

 D, was resolved into fine lines when the sun was high, but appeared 

 as a continuous band when the sun was near the horizon. 



