102 REPORTS OF INVESTIGATIONS AND PROJECTS. 



and consequent temperature distribution within and many of the conditions 

 of measurement were purposely changed in the new determination. This 

 'leaves little doubt of the absolute character of the new temperature scale. 



THE PLANT. 



Except for the addition of a 500-ton press and a hydraulic accumulator, 

 together with suitable feed-pumps and gages, no considerable change has 

 been made in the permanent equipment of the Laboratory. Dr. Albert 

 Ludwig, of Dusemond, Germany, who spent sixteen months at the Laboratory 

 as a research associate, and to whose experience we are chiefly indebted for 

 the success of the pressure plant and of the work so far undertaken with it, 

 has now finished his work and returned to Germany. 



PUBLISHED WORK OF THE YEAR. 



Brief reviews of the papers published by members of the Laboratory staff 

 during the year follow : 



(1) Ein Projections-Transporteur. V. Goldschmidt and Fred. Eugene Wright. 



Zeitschr. f. Kryst., 45, 569. 1908. 



A brief description of an apparatus for laying out in gnomonic and stereo- 

 graphic projection the position angles <^ p and v p obtained in measuring 

 crystals with the two-circle goniometer. 



(2) Das Doppel-Schrauben-Mikrometer-Okular und seine Anwendung zur Messung 



des Winkels der optischen Achsen von Krystalldurchschnitten unter dem 

 ^- Mikroskop. Fred. Eugene Wright. Tschermak Min. u. Pet. Mitth., 27, 293. 



' 1908. 



In thin sections minerals are identified and determined according to the 

 various optical properties whereby the importance of a given optical property 

 is to a certain extent dependent upon the degree of its independence of the 

 plane in which the slide is cut. In anisotropic minerals, the angle of the 

 optic axis, and therefore the optical character, is an extremely important and 

 useful diagnostic property, but until recently its measurement could only be 

 carried out upon a very limited number of sections of especially favorable 

 minerals and was therefore not generally available. Professor Becke has 

 recently devised a drawing-table by the use of which the angle of the optic 

 axes can be determined upon any thin section in which at least one optic axis 

 appears in the field, which has considerably increased the usefulness of this 

 property. This paper describes a new method by which similar measure- 

 ments can be made with a new double-screw micrometer ocular. A com- 

 parison of this method with the Becke drawing-table method shows that the 

 two are in general equally applicable and that the results in sections where 

 both axes appear in the field are more accurate than in other sections. The 

 error in this case amounts to only ±1°, while if only one optical axis is in 

 the field the probable error in the most favorable cases is 2 to 3° for the 

 micrometer ocular and 4 to 5° for the Becke drawing-table. The time re- 

 quired for the measurement is about one-half of that necessary with the 

 drawing-table and the personal equation which enters in the case of the latter 



