360 



Prof. J. Dewar. 



greater, in others less, than 1. The same irregularity has been previously 

 pointed out by Masson for the gelatin solutions of the sulphates of 

 magnesium and lithium. 



The attempt is made to explain this deviation from the requirements 

 of theory, and also the difficulty that Kohlrausch is unable to assign to 

 dyad elements any value for the specific ionic velocity, which is 

 the same when calculated from the measurements of different salts 

 of the same metal, by the assumption, first advanced by Hittorf, that, 

 in concentrated solutions of these salts ionisation takes place in such 

 a manner that there are formed complex ions in addition to simple 

 ones ; and the conclusion is drawn that, in all cases where any consider- 

 able change in transport number occurs with changes in concentration, 

 complex ions are present to a greater or less extent. 



June 13, 1901. 



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



Mr. James Mansergh, Major Eonald Eoss, Mr. Oldfield Thomas, 

 Mr. William Watson, and Mr. William C. Dampier Whetham were 

 admitted into^ the Society. 



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

 ordered for them. 



The Bakerian Lecture, " The Nadir of Temperature, and Allied 

 Problems," was delivered by Professor James Dewar, F.E.S. 



Bakerian Lecture. — The Nadir of Temperature, and Allied 

 Problems. 1. Physical Properties of Liquid and Solid 

 Hydrogen. 2. Separation of Free Hydrogen and other Gases 

 from Air. 3. Electric Eesistance Thermometry at the 

 Boiling Point of Hydrogen. 4 Experiments on the Lique- 

 faction of Helium at the Melting Point of Hydrogen. 5. Pyro- 

 electricity, Phosphorescence, &c." By James Dewar, LL.D., 

 D.Sc, F.E.S., Jacksonian Professor in the University of Cam- 

 bridge, and Fullerian Professor of Chemistry, Eoyal Institu- 

 tion, London, &c. Delivered June 13, 1901. 



(Abstract.) 



Details are given in this paper which have led to the following 

 results : — 



The helium thermometer which records 20 o, 5 absolute as the boiling 



