326 WRIGHT! CRYSTALS AND CRYSTAL FORCES 



of the true temperature 6 may be computed. From a curve of 

 U versus 6 the temperature corresponding to a luminosity of 

 6994 candles per square centimeter is found to be 3712° absolute. 

 If one uses Langmuir's values of the emissivity, the constants 

 A', p, and q have the values: A' = 0.388, p = + 0.0000079, 

 and q = 0. This gives a temperature of 3660° absolute for the 

 melting point of tungsten. 



Summary. An equation has been derived giving the relation 

 between luminosity and temperature, of a non-black body, more 

 especially a metal. This has been applied for the computation 

 of the melting point of tungsten from Langmuir's determinations 

 of the luminosity of tungsten at its melting point. The value 

 of 3712° absolute is obtained on the basis of Hyde, Cady, and 

 Forsythe's and Worthing's measurements on the color tem- 

 perature, true temperature, and apparent temperature of tungs- 

 ten. If Langmuir's values for the emissivity are used, the melt- 

 ing point is found to be 3660° absolute. Both of these values 

 are computed on the basis of c 2 = 14450 and upon Hyde, Cady, 

 and Forsythe's values of the luminosity of a black body at 

 various temperatures. 



CRYSTALLOGRAPHY.— Crystals and crystal forces. 1 F. E. 

 Wright, Geophysical Laboratory. 



The object of this paper is to state a problem, namely, that of 

 the measurement of crystal forces, and to discuss briefly some of 

 the more important phenomena which result from the action of 

 these forces and which may possibly be of value in the solution 

 of the general problem. 



A crystal is a body whose component atoms are arranged in 

 definite space lattices; this arrangement is probably the result 

 of the vectorial action of interatomic forces and, as a rule, finds 

 outward expression in the development of flat crystal faces. In 

 this definition no reference is made to the state of cohesion of 

 the body, whether solid or liquid ; nor to its homogeneity. Ordi- 

 narily these attributes are essential and are included in the 

 definition; but the discovery of liquid crystals by Lehmann has 



1 Read before the Geological Society of America on December 29, 1915. 



