GEOPHYSICAL LABORATORY. 135 



tions (cristobalite, tridymite, quartz) are built up by combining the threaded 

 triplets in three different ways, the connection between threads being through 

 the oxygen atoms. The high-low (a — ^) inversions in all the forms are 

 thought to be due to the same underlying mechanism, namely, a change in the 

 state of motion of certain electron orbits, resulting from increased thermal 

 vibration of the atoms, whereby the shape of the silica triplet and the relative 

 positions of the two oxygen atoms are suddenly altered. 



The theory as a whole gives a satisfactory explanation for many phenom- 

 ena of silica not discussed in the paper, and many phenomena not yet tested 

 experimentally are predictable from the theory. 



(477) The crystal structure of hydrazine dihydrochloride. Ralph W. G. Wyckoff. Am. 



J. Sci., 5, 15-22. 1923. 



Using Laue photographic and spectrographic data and making use of the 

 results of the theory of space groups, the manner of arrangement of the atoms 

 within the unit cell of a crystal of hydrazine hydrochloride, which contains 

 four chemical molecules and is 7.89 a. u. on a side, has been determined. 

 The parameter v defining the positions of the chlorine atoms is determined as 

 0.27-1- and the most probable value of the nitrogen parameter is estimated as 

 about 0.04. The distance between adjacent chlorine atoms thus is approx- 

 imately 3.96 A. u.; between chlorine and nitrogen atoms about 3.14 a. u. 

 It is pointed out that these results are greatly at variance with the hypothesis 

 of constant atomic radii. 



(478) The genesis of meliUte. N. L. Bowen. J. Wash. Acad. Sci., 13, 1-4. 1923. 



This paper discusses the conclusions reached by K. H. Scheumann regard- 

 ing the origin of certain rocks from Polzen, Bohemia. Scheumann applies 

 to these rocks the results of experimental work given by Bowen in connec- 

 tion with the study of alnoites occurring near Montreal. Scheumann con- 

 cludes that the production of melilite by reaction of augite and nephelite- 

 rich liquid, as advocated by Bowen, is to be regarded as supplemented by 

 actual addition of lime to the magma. It should be noted, however, that if 

 melilite were commonly produced merely by addition of hme to a magma, 

 that mineral should be found as frequently in deep-seated rocks as in surface 

 rocks. The observed absence of melilite in deep-seated rocks therefore 

 points to the dominance of the reaction method of forming it in nature. 

 Scheumann points to the supposed absence of analcite (a product of the 

 above reaction) in melilite rocks, but examination of such rocks reveals two 

 occurrences in which analcite is found, the one at Moiliili, Oahu, Hawaii, and 

 the other at Wolf Kraal House, Namaqualand. 



Scheumann's rocks have escaped the attention of many petrologists on 

 account of his use of local names, such as polzenite and modlibovite. Such 

 names, now commonly used by petrologists, are to be deplored, and an appeal 

 is made for the use of names descriptive of the actual mineralogy of the rocks. 



(479) Notes on the electric heating of calorimeters. W. P. White. J. Wash. Acad. Sci., 



13, 17-28. 1923. 



The calorimeter is most accurate when the measurements are comparative. 

 The practical working standard in the best work is nearly always a quantity 

 of heat supplied electrically. To define the calory electrically, therefore, 

 is merely to recognize an existing situation, but should avoid the needless 

 confusion which now often arises from the use of various slightly different 

 calories. 



When heat is supplied very uniformly by an electric current, the thermal 

 head of the calorimeter can advantageously be calculated without observing 

 it during the actual heating. An analysis of the errors of this form of pro- 



