( 238 ) 



Physics. - "Some remarks on the last observation* of Prof. H. 

 Kamerlingh Onnes and Dr. W. H. Keesom." By Mr. J. J. 

 van Laar. (Communicated by Prof. H. A. Lorentz). 



In the Proceedings of May 24 (1907) Prof. Kamerlingh Onnes 

 and Dr. Keesom answered some remarks winch 1 published in the 

 Proceedings of April 26 (1907) (in reference to their last papers). 



I may be allowed to revert briefly to the chief points of this 

 answer. 



n. P. 235, line 14 — 18: "It would have been good", etc. 



In fact the course of the plait in the case referred to by Prof. 

 Kamerlingh Onnes and Dr. Keesom has not been given by me. I 

 confined myself to investigating the course of the plaitpoint line in 

 general. The results which I obtained on this point harmonize fully 

 with what was found by Kamerlingh Onnes and Keesom. ') 



h. P. 236, line 7—15. 



In my papers published in These Proceedings only the case b 

 has been mentioned (in which a minimum temperature occurs on 

 the branch C a C^ of the plaitpoint line). The reason of this is, that 

 I then (7 June 1905 and 10 January 1906) only worked out 

 the case bi = b t , in which such a minimum always occurs. 2 ) 

 The formulae which I developed afterwards for the general 



case b, o 6 2 (see Teyler I, II and III), [which last publication (viz. 



Ill) was delayed by circumstances independent of my will], contained 

 the possibility of the three cases a, b and c. As a matter of 

 course Prof. Kamerlingh Onnes and Dr. Keesom could not take this 

 vet unpublished investigation into account, and I only mention the 

 fact to prove that the possibility of the cases a and c had not 

 escaped my notice. 



c. P. 236. "In our opinion, however, Mr. van Laar is mistaken 

 when he thinks that the one condition stated by him is sufficient in 

 all cases to decide as to the occurrence of a minimum plaitpoint 

 temperature." 



M At the same time I am glad to declare that 1 completely acknowledge the 

 priority of Prof. Kamerlingh Onnes and Dr. Keesom in bringing to light the possi- 

 bility of plaits which proceed without minimum from C, to C 2 and inversely 

 (cases a. and c. of Kamerlingh Onnes and Keesom), the knowledge of which is 

 necessary for understanding the behaviour of binary mixtures, containing as one 

 component a substance with weak attraction. 



l,Nole added in the English translation). 



-) Afterwards 1 have .seen that also for b i = b. 2 the case a. does occur, when 

 it is not supposed that 2' < 1\_ ■ (Note added in the English translation). 



