718 Prof. H. A. Wilson on the 



The increase in the current between one and two volts 

 with salt below the upper (negative) electrode w r as supposed 

 to show that above one volt the negative ions from the salt 

 moved down the flame. The increase in the current below 

 one volt is however quite marked. It was then supposed 

 that the flame without salt was not strongly ionized, but now 

 it is known that the small current without salt is due to the 

 great resistance close to the negative electrode, and that 

 the ions present are sufficient to carry a current of probably 

 many amperes. Such experiments, therefore, do not give 

 any information with regard to the velocity of the negative 

 ions. 



Under these circumstances it is necessary to fall back on 

 indirect evidence. Measurements of the effect of a magnetic 

 field on the conductivity of a Bunsen flame made by the 

 writer* indicated that the velocity of the negative ions was 

 about 9000 cms. per sec, which is about the value to be 

 expected for negative electrons. 



We may therefore conclude that the positive ions of 

 alkali salts in flames are probably single atoms of the metal, 

 and that the negative ions are electrons. 



In a recent paper Mr. Lusby t finds 290 cms. per sec. for 

 the velocity of the positive ions of salt vapours in flames. In 

 his experiments the electrodes were only 3 cms. apart, so that 

 in the absence of salt the uniform gradient was not present 

 because the negative drop extends more than 2 cms. from the 

 lower electrode. On putting in the salt near the upper 

 electrode he observed a very small uniform gradient which 

 is evidently due to the high conductivity of the salt vapour. 

 To calculate the velocity of the ions correctly the value of 

 the uniform gradient just below the salt vapour is required, 

 and this should be equal to the gradient in the absence of 

 salt since the current is unchanged at the critical potential. 

 I think therefore that Mr. Lusby's result is too high. 



LXXXIV. The Nwtriber of Electrons in the Atom. By Prof. 

 H. A. Wilson, F.B.S., F.E.S.C., McGill University, 

 Montreal %. 



ACCORDING to Sir J. J. Thomson's theory § atoms may 

 be regarded as spheres of positive electricity containing 

 negative electrons which can move about freely inside the 

 positive charge. The total negative charge on the electrons 



* Proc. Roy. Soc. A., vol. lxxxii. 



t Prcc. Camb. Phil. Soc. vol. xvi. Pt. 1, 1911. 



t Communicated by the Author. 



§ 'The Corpuscular Theory of Matter/ 1907, 



