468 



Professor Dewar 



[May 10, 



WEEKLY EVENING MEETING, 



Friday, May 10, 1889. 



William Crookes, Esq. F.R.S. Vice-President, in the Chair. 



Professor Dewar, MA. r.R.S. M.B.I. 



Optical Properties of Oxygen and Ozone, 



In the course of experiments on the spectra of gases at high pressures, 

 Professor Liveing and I have made observations on the absorption- 

 spectrum of oxygen which confirm and extend the observations of 

 Egoroff and Jansen. The interest of this spectrum is so great, on 

 account of the important part which oxygen plays in our world, and 

 its free condition in our atmosphere, that it deserves a separate 

 notice. 



In order to include the ultra-violet rays in our observations we 

 have had to contrive windows of quartz to the apparatus containing 

 the gases. A strong steel tube, 1G5 centimetres long and 5 centi- 

 metres wide, was fitted with gun-metal ends, bearing by curved 



Fig. 1. 



Section through one end of the tube. 



surfaces upon the conical openings of the tube, and forced home by 

 powerful screw-caps. Each gun-metal end was pierced centrally by 

 a conical opening fitted with a quartz stopper, 2*1 centimetres thick, 

 and of the same diameter, with plane polished ends. A small amount 

 of wax was interposed between the stopper and the gun-metal for the 

 purpose of ensuring a uniform bearing for the quartz, which is very 

 brittle. Trial proved that the tube thus fitted would sustain, without 

 leakage, a pressure of upwards of 260 atmospheres. The tube had, 

 besides, near each end, a screw-j^lug valve for admitting the gases. 

 About the centre of the tube was placed a quartz lens, rather less 

 in diameter than the tube, held in place by three sinings which 

 pressed against the walls of the tube. This lens had a focal 

 length of about 46 centimetres ; so that when a source of light was 



