1897.] the compression of certain rarified Oases. 301 



discharges in large bulbs than in small tubes, I could not get the 

 discharge to pass. The failure was attributed to the fact that the 

 inner walls of the bulb were always wet with strong sulphuric 

 acid, some of which floated on the surface of the mercury. 



23. It may be noted here that the mercury in the pump was 

 connected with earth through wires and the gaspipe system. 

 This fact constitutes a difficulty in the way of explaining the 

 pressure-glow as simply a phenomenon of electrical origin in which 

 the compression plays a secondary part. 



24. The explanation of the pressure -glow appears to me 

 rather to be in general agreement with the explanation given by 

 Sutherland {Phil. Mag. 1897, Mar.) of anomalies observed by 

 Bohr and Crookes in the compression and rarification of oxygen. 

 According to Sutherland, in the rarification of oxygen a point is 

 reached (pressure mm, 7) when oxygen begins to be converted into 

 ozone, and below the pressure mm "15 the gas is entirely 

 ozone. Between the pressures 15 mm and mm 7 the gas obeys 

 Boyle's Law as oxygen, and below mm, 15 it obeys Boyle's Law as 

 ozone. Between the pressures mm -7 and mm- 15 the gas is a 

 mixture of oxygen and ozone. Sutherland is led to the view that 

 in the compression of ozone from the lowest pressures, the ozone 

 begins, when the pressure reaches the value mm '15, to be knocked 

 to pieces in virtue of the frequency of collision between ozone 

 molecules being the same as that of some natural vibration in the 

 molecule. 



25. If Sutherland's views be correct in the case of ozone and 

 oxygen, it is probable that there must follow a generalization of 

 them to cases where mixtures of different gases are concerned. 



[Since the subject of this note was communicated to the 

 Society, an abstract has appeared of a paper by Prof. Threlfall 

 and Miss Martin (Nature, Vol. 56, p. 288) in which an experiment 

 was made with the object of investigating whether oxygen can 

 form ozone simply by virtue of a reduction of pressure, and the 

 authors come to the conclusion that either no ozone is formed, or 

 if such formation does occur, it is to an extent less than 0005 per 

 cent, of the volume of the gas employed. The nature of the 

 indicator is not described in the abstract referred to.] 



Spectrum of the 'pressure-glow. 1 



26. The spectrum of the gas glowing during compression is 

 very marked and consists of a faint continuous spectrum with 

 four conspicuous bright bands coinciding with those which 

 Schuster has described as belonging to the spectrum of the nega- 

 tive glow of oxygen. 



