SECTIONAL TRANSACTIONS. 



(For reference to the publication elsewhere of communications entered in the 

 following lists of transactions, see end of volume, preceding index.) 



SECTION A. 

 MATHEMATICAL AND PHYSICAL SCIENCES. 



Thursday, September 1. 



Prof. A. M. Tyndall. — The mobility of positive ions in gases. 



It has been shown by Powell and the author that minute traces of impurity 

 may have a striking effect on the mobility of positive ions in a gas. Changes 

 in the nature of the ions may be brought about by (i) the formation of a 

 cluster of impurity molecules around the ion ; (2) the production of ions 

 of the impurity by collisions of the second kind ; (3) the phenomenon of 

 electron exchange. 



When sources of positive alkali ions are employed traces of impurity are 

 less critical because of the low ionisation potential of these metals. A study 

 of the mobility of these ions in various gases has led in certain cases to a 

 simple law connecting the mobility of an ion with its mass. The apparatus 

 then becomes analogous to a mass spectrograph in that it may be used to 

 analyse the ions emitted by a given source. When the source of ions is a 

 glow discharge the high gas pressures employed permit of the study of 

 types of collision processes relatively infrequent at the low pressures more 

 commonly employed. 



Sir R. T. Glazebrook, K.C.B., F.R.S., and Dr. L. Hartshorn. — 



Material standards of resistance : the B.A. Coils, i88i-ig32. 

 [Ordered by the General Committee to be printed in extenso. See p. 417.) 



Joint Discussion with Section J (Psychology) on The quantitative relation 

 of physical stimuli and sensory events (Mr. T. Smith, F.R.S., Prof. J. 

 Drever, Dr. J. H. Shaxby, Dr. Wm. Brown, Dr. R. A. Houstoun, 

 Mr. R. J. Bartlett, Dr. S. G. Barker and Mr. C. G. Winson. 

 Experimental demonstration by Dr. L. F. Richardson, F.R.S.) : — 



Prof. J. Drever. 



The world of sense is at once physical and psychological. The general 

 problem of physical science is the more adequate understanding of the world 

 of sense, and this is also a problem for the psychologist. The physicist 

 studies the processes and patterns of the world of sense as they appear to 

 determine one another independently of the individual observer, the psycho- 

 logist the processes and patterns as they determine the sensory world as 

 experienced. The correlation of the sense experience of the individual 

 with the processes and patterns investigated by the physicist presents a 



