( 573 ) 



Finally I must ineiiliou (hat, on llic occasion of a later visit to 

 the loani-pi( near Henieluui, I fonnd l\vo more erratic-blocks, which 

 must probably also be counted amonu; [)ieces of Disci neUa Holsli- 

 sandstone. Neither contains any fossils. One corresponds petrogra- 

 phically with what was described ; the otiier is foi- the greater 

 part while, but possesses green layers. If I aui uol mistaken, I 

 sometimes saw suclilike stones on the beach of l>orgliobu. 



Physics. — "(hi the coiii'se of the rdlncs of h for hi/drof/eii, In 

 coiiitcdio]} irith a recent joi-iinihi of Prof, van dkr Waals." 

 Hv Dr. J. J. VAN Laar. (Communicaled by Prof. ^. D. van dkk 



Waals). 



1. Making use of the tlieory of cijcUc motions, Prof, van dkr 

 Waai-s has given a new deduction of the equation of state of a 

 simple substance, in which the size of the molecule ai)i)eai-ed to be 

 variable, and to be a function of the volume ^). 



For a bi-atomic gas the following formula has i)een found: 



^-ii^^i-r^Y (1) 



Here h^ denotes the smallest value of b, corresponding to the case 

 that the two atoms of a molecule touch each other; h^j represents 

 the greatest xalue i. e. the value for very great (inlinitely great) 

 volume. The above equation may be easily deri\ed from the so 

 called "equation of state of the molecule" : 



(/>-/>)= UT {n) 



V' 



when we take r = cc, in which case /> assumes the value A,, and 

 n A- — mav be neglected with respect to a{l) — h). So we get: 



If we substitute this value into equation {<i), paying regard to 



a RT 



P + 3 



we get the e(j nation 



\v-h {l>g — 0,) J 



which yields immediately equation (1). 



1) These Proceedings of the meetings of February, March and April 1901. 

 See also "Livre jubilaire dédié a J. Bosscha" of the Arch. Ncerl., p. 47. (The 

 first communication and pait of the second di?cuss principally the specific heat 

 for very large volume). 



