GEOPHYSICAL LABORATORY. 143 



over a narrow aperture, focus on it a strong beam of light through the aper- 

 ture, and observe the differences in degree of transparency as the pearl is 

 rotated, (b) Stand with the back toward a window or other source of Hght and 

 observe, on rotating the pearl, that in certain positions the characteristic 

 mother-of-pearl sheen is visible, shining out from inside the pearl, (c) 

 (Modification of the Galibourg-Ryziger method). Observe with the aid of a 

 microscope the walls of the hole drilled through the pearl as seen reflected by 

 a small bead at the end of a fine gold wire as it moves through the hole. At 

 the boundary between the mother-of-pearl bead and the enveloping nacre 

 substance there is an appreciable change in intensity of illumination which is 

 characteristic of the cultivated pearl. 



(500) The residue from silica in rock-analysis. M. Aurousseau. J. Wash. Acad. Sci., 



13, 330-332. 1923. 



The residue remaining after the driving off of silica by hydrofluoric acid was 

 analyzed and was found to be composed principally of the oxides of titanium, 

 iron, magnesium, and aluminum, with small amounts of lime, phosphoric 

 oxide, and sulphur trioxide. The bearing of these results on rock-analysis is 

 discussed. 



(501) A comparison of the heating-curve and quenching methods of melting-point determi- 



nations. George W. Morey. J. Wash. Acad. Sci., 13, 326-329. 1923. 



The heating-curve method, which is the method followed almost exclusively 

 in the study of metals and of salts which crystallize readily, is compared with 

 the quenching method, used chiefly in the study of substances which are diffi- 

 cult to crystallize, such as most silicates. It is well recognized both in theory 

 and practice that the melting-point of a substance of the latter class is more 

 accurately determinable by the quenching method. Taking the melting- 

 point determination by this method as the standard, it is shown that the true 

 melting-point lies on the more rapidly rising end portion of the heating curve. 

 As usually interpreted, therefore, the heating-curve method tends to give a 

 melting-point which is too low. The difference in the present case (sodium 

 metasilicate) is of the order of magnitude of 2° or less at about 1100°. 



(502) Petrology of the Hawaiian Islands: III. Kilauea and general petrology. Henry S. 



Washington. Am. J. Sci., 6, 338-367. 1923. 



In this third installment of the series the lavas of Kilauea are described, 

 with eight new analyses. The ancient lavas differ texturally from the recent 

 ones, but they are all rather uniform in chemical and mineral composition, 

 mostly ordinary basalts, with or without olivine, and fewer picrite basalts. 

 In the second part of the paper the relative ages of the five volcanoes are 

 shown to be: Kohala, Mauna Kea, Hualalai, Kilauea, and Mauna Loa, the 

 last two being thought to be connected. The occurrence of the various types 

 of lava and their succession at the different volcanoes are discussed and the 

 calculated average chemical compositions of the lavas of each volcano are 

 given. The trach3rtes of Puu Waawaa and Puu Anahulu are thought to be 

 connected with Kohala, not with Hualalai. Daly's views on the origin of 

 the trachytic lavas and of the picrite basalts and the dunitic xenoliths are also 

 discussed. 



(504) On the existence of an anomalous reflection of X-rays in Laue photographs of crystals. 

 Ralph W. G. Wyckoff. Am. J. Sci., 6, 277-287. 1923. 



Spectrometric and Laue photographic observations by G. L. Clark and W. 

 Duane upon crystals of potassium iodide have been thought to point to the 

 existence of intense diffraction effects which were incapable of explanation 

 on the basis of existing theory. The experiments here described record the 

 inability to find any evidence for these anomalous effects upon numerous 



