839 
known, or at least until we know how long the increase, which 
began a few years ago, will last. 
The accompanying diagram shows for the years 1847 to 1912 the 
excess of the observed longitude of the moon over Newcoms’s great 
fluctuation, 1. e. the number contained in the fourth column of Table VII. 
Ross’s curve is also given, (including the constant term — 0".18). 
The broken line is the smooth curve mentioned in Part I from 
which the values given in Table III were read off. The diagram 
also contains the purely periodic part As; and 2’, of the perturbation 
in longitude produced by the absorption of gravitation on the two 
hypotheses regarding the distribution of density within the earth. 
Chemistry. — “The equilibrium Tetragonal Tin S Rhombic Tin.” 
By Prof. Ernst COHEN. (Communicated by Prof. vaN ROMBURGH). 
(Communicated in the meeting of November 30, 1912). 
It has struck me, and from several quarters my attention has 
been called to it, that in a communication from Mess Smits and 
pr Leeuw 5) “On the system Tin” there occur a number of mistakes 
which require rectification. 
1. The relation between the existence of a transitionpoint tetra- 
gonal tin SS rhombic tin at 200° and the method of preparation of 
the so-called corn-tin or grain-tin has been first pointed out in the 
paper which I lave published in 1904 with Dr. E. Gonpscumipt *). 
From the communication of Mess's Smits and pr Lrruw the reader 
might conelude that they (or ScHaum) have first notieed this connection, 
2. In the paper which I published in 1904 with Dr. E. Gorp- 
SCHMIDT, a conclusion was drawn, from the experiments of WeERIGIN, 
LEWKOJEFF, and TAMMANN*) as to the situation of the said transition 
point. which proved to be erroneous. Dr. DrGeNs has pointed this 
out ‘) and as in my opinion he was quite right. | have hastened to 
rectify my error in the section of ABrGe's Handbuch der anorganischen 
Chemie | Vol. 3, (2) 532 (1909), special p. 552 | edited by myself, 
Evidently, the recent literature on this subject has not been known 
to Mess's Smits and pe Leeuw, for they still base their communication 
on my paper that appeared five years previously. 
1) These Proc. XV, p. 676. 
2) Chem. Weekblad 1, 437 (1994), special p. 446. Zeitschr. f. physikal. Chem, 
BO, 225 (1904), special p. 234. 
3) Drud. Ann. 10, 647 (1903). 
4) Dissertation, Delft 1908, p. 35. 
