﻿772 Mr: J. H. C. Searle on the 



These results point to the fact that the atom of chlorine 

 does not easily lose an electron, and this is what might be 

 expected from its electronegative character. Affinity for 

 negative electricity is the characteristic of electronegative 

 elements. Hydrogen is a borderland element, taking up a 

 position among the noble metals in virtue of its electro- 

 chemical properties ; it is distinctly more electropositive than 

 copper, however, even at ordinary atmospheric pressure, and 

 this is more marked at higher pressures, A possible explan- 

 ation of the reaction between hydrogen and chlorine is that 

 an atom of hydrogen, under the influence of ultra-violet light, 

 emits an electron which immediately becomes attached to an 

 atom of chlorine and chemical combination takes place *. 

 There is some support for this hypothesis in the fact that the 

 presence of hydrogen enormously increases the number of 

 ions emitted by hot platinum and by the alkali metals at 

 ordinary temperatures. 



The fact that in many cases minute traces of foreign 

 matter are requisite both for the ionization of gases and for 

 their chemical combination is very striking ; the two actions 

 are probably either cause and effect or are attributable to 

 some common cause. However this may be, it appears that 

 actual liberation of electrons for any measureable period of 

 time is not a necessary precursor of gaseous combination. 



In conclusion I must express my indebtedness to Prof. 

 Lenard for his kindness in allowing me to work in the Radio- 

 logical Institute or! the University of Heidelberg and for his 

 guidance while the work was in progress. My thanks are 

 also due to Prof. Becker and Dr. Hamsauer for kind assistance 

 and advice. 



Clifton College, Bristol. 



LXXY. The Problem of the Weir. By J. H. C. Searle, 

 J3.Sc, Assistant Lecturer in Mathematics in the Victoria 

 University, Manchester f. 



§ 1. HPHE problem of determining the motion of a stream 

 JL flowing in a horizontal channel, whose bed is 

 subject to slight inequalities of level, was investigated by 

 Lord Kelvin J, who assumed the flow to be irrotational, and 

 obtained an approximate solution of the motion. Wien §, 



* Lenard and Pauisauer suggest that the light splits up the chlorine 

 molecule into its two neutral atoms. 



t Communicated bj Prof. Horace Lamb, F.R.S. 

 t Phil. JUag. [5] vol. xxii. p. 353 et seq. 

 § Wien, Hydrodynamik, p. 201. 



