GEOPHYSICAL LABORATORY. IO3 



method does not enter in the former. Meanwhile, both methods ought to be 

 considered as approximate, giving good results only under the most favorable 

 conditions, where the axial bars are sharply developed and the influence of 

 double refraction can be neglected. 



(3) Artificial daylight for use with the microscope. Fred. Eugene Wright. Am. 



Journ. Sci. (4), vol. 27, 98. 1909. 



An account of the successful employment of acetylene light, a large con- 

 densing-lens, and a pale-blue glass ray-filter in place of daylight, with the 

 petrographic microscope. 



(4) A new goniometer lamp. Fred. Eugene Wright. Am. Journ. Sci. (4), vol. 27, 194. 



1909. 



A convenient arrangement for the use of an acetylene flame in goniometric 

 measurements upon minute crystal faces. It has proved to be more generally 

 serviceable than the electric arc or the Nernst glower, is inexpensive, and 

 can be assembled in a few hours from the resources of any shop. 



(5) A containing device for salts used as sources of monochromatic light. Fred. 



Eugene Wright. Am. Journ. Sci. (4), vol. 27, 194. 1909. 



The device consists of a small platinum crucible (about 2 cc), which can 

 be attached to a Bunsen burner in such a position that the flame plays upon 

 one side of the crucible and keeps the salt melted. From the interior of the 

 crucible a bundle of small platinum wires extends out into the flame and 

 serves as a wick. The flow of material is continuous and the flame remains 

 constant for long periods of time without attention. 



(6) Ueber die Anwendbarkeit des Nernstchen Warmetheorems auf einige heterogene 



Gleichgewichte. John Johnston. Zeitchr. f. Phys. Chem., 65, TzT- IQOQ- 



The application of strict thermodynamic principles to the calculation from 

 existing experimental data of the free energy changes attending the formation 

 of certain carbonates, hydroxides, and oxides leads to results which exhibit 

 satisfactory concordance between calculated and experimental values; the 

 Nernst approximation formula, however, applied to the calculation of the 

 same heterogeneous equilibria, does not in general give correct results, and 

 hence it is to be classed as an empirical rule along with the similar rules of 

 Le Chatelier and de Forcrand. 



(7) Quartz as a geologic thermometer. Fred. Eugene Wright and Esper S. Larsen. 



Am. Journ. Sci. (4), vol. 27, 421. 1909. 



In this paper attention is directed to a geologic thermometer-scale the 

 points for which are to be sought in the stability ranges of the different 

 phases of rock-making minerals (their melting and inversion temperatures), 

 and also in the melting temperatures of certain mineral aggregates (eutec- 

 tics). Quartz is well adapted to furnish at least one and possibly two points 

 for the geologic thermometer scale, since on heating at 575° it suffers an 

 enantiotropic change to a second phase, called /8-quartz by Miigge, while 

 above 800° it is no longer stable at ordinary pressures, but passes into tridy- 

 mite. Following the example of Le Chatelier and Mallard, the point of in- 

 version of a and j8 quartz was redetermined by observing the abrupt change 

 in the birefringence, circular polarization, and expansion coefficient at that 

 temperature. The most accurate optical determinations place this inversion 



