Law of Pressure of Gases between 75 ami 100 turn. 495 



February 27, 1902. 

 Sir WILLIAM HUGGINS, K.C.B., D.C.L., President, in the Chair. 



A List of the Presents received was laid on the table, and thanks 

 ordered for them. 



The Bakerian Lecture, "The Law of the Pressure of Gases," was 

 delivered by Lord Rayleigh, F.R.S. 



The following Paper was read : 



" Note on the Discovery of a New Trypanosoma. ' By Lieut. -Colonel 

 DAVID BRUCE, R.A.M.C., F.R.S. 



BAKERIAN LECTURE. "On the Law of the Pressure of Gases be- 

 tween 75 and 150 Millimetres of Mercury." By Loim 

 RAYLEIGH, F.R.S. Received January 15, Read February 27, 

 1902. 



(Abstract.) 



The observations here recorded were intended to bridge over in 

 some degree the gap between the very low pressures (below 1-5 nun.) 

 dealt with in a recent paper and pressures approaching the atmo- 

 spheric for which the usual mercury column and cathetometer method 

 is adequate. The principal novelty consists in the use of two similar 

 manometric gauges. Pressures in the ratio of 1 : 2 are obtained 

 by the use first of a single gauge and secondly of the two gauges 

 connected in series. The equality of the gauges is tested by obser- 

 vations upon them when combined in parallel. The use of these 

 gauges allows abundant accuracy in the measurement of the pres- 

 sures, and the difficulties relate rather to the adequate determina- 

 tion of volumes and temperatures. 



The results show that, to an accuracy of ^tnn> a ^ r hydrogen, oxy- 

 gen, and argon obey Boyle's law. In the case of nitrons oxide a 

 deviation was observed in the direction that might be expected. 



