( 201 ) 



value of T las alixady sinpassed this limit. The fact that such a 

 maximum value exists may be understood, if we consider that a 

 gas under a constant pressure is ever more rarefied, when the 



temperature rises — so that at 2'= infinite, a pressure = -'— 



' ^ 76 



would require an infinite volume, and correction would bo un- 

 necessary. 



The condition for the observation under a pressure of — , without 



^ 76 ' 



the vapour being' saturated is, that T must not descend below a 



Tk 



certain limit, which we shall put at . 



' ^ 1,6 



For -— r=l,6 we find -—, r= 1—0,0116, so that the normal density 



is more than 1 pCt. smaller than that which is furnished bv the 

 observation. 



If the assumption of cu = « - agrees better with the observations, 



than the su])position that a is constant, we should have to put: 



-^ = 1—0,001645 -—) — (_A) _i 



rr 



in which case for — ^=1,6 the normal density would be more 

 than 2 pCt. smaller than would follow from the observations. 



Astronomy. — y,Some remarks upon the li-monthhj motion of the 

 Pole of the Earth and upon the lencjth of its period". By 

 Dr. E. F. VAN DE Sande Bakhuyzen (Communicated by 

 Prof, H. G. VAN DE Sande Bakhuyzkn). 



(Read in tlie Meeting- of October 29'!^ 1898). 



1. In the recent N"^. 440 of the Astronomical Journal another 

 essay is given by Dr. Chandler on the motion of the Pole of the 

 Earth, in which he discusses the observations performed in the years 

 1890 — 1898 and employs the older series to investigate anew the 

 length of the 14-mouthly period. On this last point he contends the 

 opinions formerly emitted by H. G. van de Sande Bakhuyzen 

 and recently by me (Proceedings of the Royal Academy, Amsterdam. 

 June 1898). To this latter paper he devotes a note running as follows : 



„The memoir last referred to did not arrive until the present 



14* 



