GHOPHYSICAL LABORATORY. IO3 



An application of the bi-quartz wedge-plate, together with an artificially- 

 twinned quartz-plate or wedge, to the accurate adjustment of the petrographic 

 microscope is considered in outline in the second part of the paper, and a 

 method of procedure for accomplishing the same indicated. 



In part 3 a simple device for holding and rotating small crystals for the 

 purpose of determining extinction angles, or for measuring optic angles di- 

 rectly, is described briefly, such an apparatus having been found peculiarly 

 useful in work with artificial crystals. 



(6) The bi-quartz wedge-plate applied to polarimeters and saccharimeters. Fred. 



Eugene Wright. Amer. Jour. Sci. (4), 26, p. 391, 1908. 



The bi-quartz wedge-plate is suggested as a simple and effective basis for 

 the construction of a polarimeter of adjustable sensibility in which the error 

 from the asymmetry of the Lippich system, together with all the serious com- 

 plications of mechanism, are completely avoided without loss of accuracy. 

 Such a plate has been constructed and successfully applied to the exact loca- 

 tion of crystal extinctions, but unfortunately pressure of other duties pre- 

 vented the actual construction of a new saccharimeter. Through the courtesy 

 of Dr. Frederic Bates, of the U. S. Bureau of Standards, however, an oppor- 

 tunity was given to test the wedge on a large and accurate standard polari- 

 meter illuminated by homogeneous green light from a mercury quartz-glass 

 arc. Its performance was entirely satisfactory, minute displacements of the 

 analyzer from its position of total extinction being readily observed. 



(7) Some new measurements with the gas thermometer. Arthur L. Day and J. K. 



Clement. Amer. Jour. ,Sci. (4), 26, p. 405, 1908. 



The gas-thermometer problem at the present stage of its development has 

 become primarily a problem for experimental study with two definite pur- 

 poses — one to increase the accuracy of the measurements, the other to increase 

 their range. The general relations involved are no longer subject to serious 

 question. The progress of recent years has given us electric heating in place 

 of gas and the consequent possibility of regulating the temperature with great 

 certainty and exactness. It has also given us the metal bulb, with a definite 

 and measurable expansion coefficient which is capable of holding the expand- 

 ing gas without loss. It has discovered a gas which does not diffuse through 

 the bulb or react with it chemically, which does not dissociate within the lim- 

 its of practicable measurement, and of which the expansion can be expressed 

 with a reasonable certainty in terms of the Kelvin thermodynamic scale. This 

 was the situation in 1900, at the time of the publication of the now generally 

 accepted high-temperature scale covering the region from 250° to 1,150° C, 

 with a probable accuracy of 5°. 



Starting from this point in 1904, Professor Holborn, of the Reichsanstalt, 

 increased the range of this scale to 1,600° C, the probable error of the new 

 portion being about 10°. Simultaneously with this effort, work was begun 

 at the Geophysical Laboratory in Washington, with a view to increasing the 

 accuracy of the scale, first over the existing range (to 1,150°), and later, as 

 much beyond this point as it should prove possible to go. Temperature meas- 

 urements between 250° and 1,150° have been made and form the subject of 

 the present paper. The particular points to which we have given the most at- 

 tention are the following: (i) To provide a uniform temperature along the 

 bulb by a suitable arrangement of the heating coils. (2) To inclose the fur- 



