584 



A. SMITS: "On Critical Endpoints in Ternary Systems" III. fCoitimunicated by Prof. J. D. VAN DER 



WAALS), p. 793. 

 A. Smits and C. A. LOBRY DE Bruyn: "The Periodic Passivity of Iron". (Communicated by Prof. 



J. D. VAN DER WAALS), p. 807. .With 2 platesL 

 F. ROELS: "On after-sounds". (Communicated by Prof. A. ZWAARDEMAKER), p. 811. 



F. A. H. SCHREINEMAKERS: "In-, mono- and divariant equilibria" III, p. 820. 



0. HOLST: "On the measurement of very low temperatures. XXVI. The vapour-pressures of oxygen 

 and nitrogen according to the pressure-measurements by V. SIEMENS and the temperature- 

 determinations by KAMERLINOH ONNES c. s.". (Communicated by Prof. H. KAMERLINOH OnneS', 

 p. 829. 



J. E. Verschaffelt: "The viscosity of liquefied gases". 1. The rotational oscillations of a sphere 

 in a viscous liquid ' (Communicated by Prof. H. KAMERLINOH ONNES), p. 840. 



J. E. VERSCHAFFELT: "Ibid." II. On the similarity of the oscillations of spheres in viscous liquids''. 

 (Communicated by Prof. H. KAMERLINOH ONNESl p. 860. 



W. H. Keesom: "Two theorems concerning the second virial coefficient for rigid spherical mole- 

 cules which besides collisional forces only exert CoULOMB-forces and for which the total 

 charge of the active agent is zero". (Communicated by Prof. H. KAMERLINOH Onnes , p. 868. 



G. Holst and L. HAMBUROER: "Investigation of the equilibrium liquid-vapour of the system 

 argon-nitrogen". (Communicated by Prof. H. KAMERLINOH OnneSi. p. 872. 



Petrography. — " Pnemiiatoli/iic hornfds from the hill countries of 

 Sink [Sum 1 1 tra)" . By Dr. H. A. Brouwer. (Communicated by 



Prof. G. A. F. Moi.ENGRAAl'F.) 



(Communicated in the meeting of October -SI, 1914). 



Tfie coiitact-plienomena desei-ibed in a former communication, ') 

 on the southwestern side of the granitic area of Rokaii are marked 

 by tlie occurrence, near the granites, of stratified granite-apophyses 

 and schistose hornfels rich in felspar. From a preliminary exami- 

 nation of the hornfels near tlie contact with granites from the hill 

 countries of Siak these rocks appear to show an entirely different 



') H. A. Bbouwer, "On the granitic area of Rokan (Middle-Sumatra) and 

 on coiitact-phenomena in the surrounding schists'', tliese Proc. Vol.XVil (1915), 

 p 1190. 



To the facts related there can be added that during an expedition along the 

 Rokan Kiri when its level \v;is low, also to the right side of the Rokan similar 

 phenomena were observed on the south-western contact of the •granites, as were 

 described from the S' ' Pakis. The first granites form an isolated little rock 

 emerging from the water near the right bank, whereas about 15 m. down the 

 river the ccntactmfetamorphic schists with numerous granite-apophyses, which 

 occur in alternating layers with the schists, are uncovered in the right bank of the 

 river. Apophyses with a thickness varying from a few cm. to at least 1 m. were 

 observed, the dip is again towards the gianitic mass (e. g. Str. N. 20 W. dip 

 N. 0. 70° was measured). As a rule, the granite of the apophyses, just like near 

 Pakis, is very rich in biotite and shows parallel texture; here too, at a short 

 distance of the zone of apophyses, lencocratic granites with parallel texture are 

 found, beds of coarse and fine-granular rocks sometimes alternate. The thickness 

 of these beds varies from a few cm. to several lim , they have almost the same 

 strike and dip as the hornfels and granite apophyses (e. g. Str. N. 30 W. dip 

 N.O. 55°). 



