PROCEEDINGS OF SECTION A. 31 



The number of ions due to impact increases with the 

 velocity of impact, but only very slowly if the velocity 

 exceeds a certain value. 



The velocity, in an electric field, of the negative ions due 

 to impact is slightly greater than that of the positive 

 ions, the ratio of the velocities being roughly 17 to 13. 



The ions rapidly recombine. the number falling to half its 

 value in five seconds from the time of impact and being 

 quite insignificant after the lapse of two minutes. 



The effect appears to vary with the nature of the material 

 of the target. 



3.— ON A SIMPLE LABORATORY METHOD OF DETERMINING THE 

 RATIO OF THE TWO PRINCIPAL ELASTICITIES OF AIR. 



By E. F. J. LOVE, M.A., D.Sc, F.R.A.S., assisted by G. SMEAL, B.Sc. 



Abstr.\ct. 



The method is in principle the same as Manoeuvrier's, but 

 differs altogether from it in details, being far simpler and at the same 

 time more flexible. True adiabatic compressions are used, and the 

 thermal difficulties of the experiment are eliminated by the use of 

 pressure changes of the order 0-06 cm of mercury, and consequently 

 temperature changes of the order 0-06°C. The results, given in 

 the paper, are claimed by the author to compare very favourably 

 with any others obtained with simple apparatus; he proposes to 

 adapt it to determine the ratio for other gases, especially hydrogen, 

 for which its freedom from thermal troubles renders it particularly 

 well adapted. 



The titles of the following papers were ordered to be 

 published :— y^jC^Q^Z 



4.— STANDARDS OF ELECTROMOTIVE FORCE. j(S' ^*-'* ^^i 



5.— COMETS AND THEIR TAILS. 



By T. COOKSEY, Ph.D., B.Sc. F.I.C. 



I, ^ . • C^ SJ ^ f^ 



-if 

 6.— THE HARMONIC ANALYSIS OF TIDAL OBSERVATIONS. ^ 



By C. E. AD A.MS, M.Sc. 



7.— TIDAL PREDICTIONS. 



By C. E. ADAMS, M.Sc. 



-THE TIME CONTROL OF THE WELLINGTON TIDE GAUGE. 



Bv C. E. ADA.MS,M.Sc. 



