KONINKLIJKE AKADEMIE VAN WETENSCHAPPEN 
TE AMSTERDAM, 
PROCEEDINGS OF THE MEETING 
of Saturday September 27, 1902. 
DC kt 
(Translated from: Verslag van de gewone vergadering der Wis- en Natuurkundige 
Afdeeling van Zaterdag 27 September 1902, Dl. XI). 
COT EEE AT LS: 
A. H. Sirks: “On the advantage of metal-etching by means of the eleetrie current”. (Com- 
municated by Prof. J. L. C. SCHROEDER VAN DER Kork), p. 219, (with one plate). 
J. D. van per Waars: “On the conditions for the occurrence of a minimum critical temperature 
for a ternary system”, p. 225. 
W. H. Kersom: “Reduction of observation equations contaiaing more than one measured 
quantity”. (Communieated by Prof. IT. KAMERLINGH Onyes), p. 236. 
E. H. M. Beekman: “On the behaviour of disthene and of sillimanite at high temperature”. 
(Communicated by Prof. J. L. C. SCHROEDER VAN DER Kok), p. 240, (with one plate). 
L. II, Siertsema: “Measurements on the magnetic rotation of the plane of polarisation in 
liquefi:d gases under atmospheric pressure. IT. Measurements with methylehloride”. (Communi- 
euted by Vrof. H. Kameruixcu ONNES), p, 243. (with one plate). 
H. Haca and C. WH. Wip: “Diffraction of Röntgen-Rays”, (2nd Communication), p. 247, 
(with one plate). 
H. A. Lorentz: “The fundamental equations for electromagnetic phenomena in ponderable 
bodies, deduced from the theory of electrons”, p. 254. 
E. F. van pr SANDE Bakuuyzen: “Preliminary investigation of the rate of the standard- 
clock of the observatory at Leyden, Hohwü Nr. 17 after it was mounted in the niche of the 
great pier”, p. 267. 
The following papers were read: 
Physics. — “On the advantage of metal-etching by means of the 
electric current’. By Mr. A. H. Siks. (Communicated by 
Prof. J. L. C. SCHROEDER VAN DER Kork). 
(Communicated in the meeting of June 28, 1902). 
Side by side with the tension- and bending-tests to which metals 
and their alloys are submitted, with the object to find out, whether 
the material answers to the requirements, Prof. BEHRENS gives, as a 
new method: a miscroscopic examination, which is deservedly made 
15 
Proceedings Royal Acad. Amsterdam. Vol. V. 
