Geology and Natural History. 499 



7. On Joints in Magnetic Circuits. — Prof. Ewing shows the 

 great effect of joints in reducing the residual magnetism of iron. 

 The division of a ring 30 cm long into two half rings abutting 

 against each other with the smoothest possible joints has the effect 

 of reducing the residual magnetism from 9,000 to 6,000. "A sim- 

 ilar reduction occurs in magnetic tests of bars when these are 

 made to form part of a magnetic circuit by the addition of a ma- 

 rine iron yoke." — Phil. Mag., Oct., 1892, pp. 320-326. j. t. 



8. Measurement of high temperatures. — Luc wig Holboen and 

 Willy Wien discuss the electrical methods of measuring high tem- 

 peratures and give results obtained by the use of a thermo-ele- 

 ment of platinum and platinum-rhodium. This method appears 

 to be preferable to Siemens's method of observing change in elec- 

 trical resistance. The authors obtain concordant results for the 

 melting point of gold, silver and copper. — Ann. der Physik unci 

 Chemie, 1892, No. 9, pp. 107-134. J. t. 



9. Color Photography. — Lippmann by the aid of a very sensi- 

 tive bromide of silver albumen plate, made orthochromatic by a 

 solution of azalin and cyanine has succeeded in photographing the 

 solar spectrum. Also a colored church window, a parrot, and 

 other colored objects. The time of exposure with sunlight and 

 the electric light varied from five to ten minutes. With diffuse 

 light an exposure of several hours was necessary. — Comptes 

 Penclus, cxiv, p. 961, 962, 1892. J. t. 



10. Electrical Resistance of Metals at Low Temperatures. — Prof. 

 Dewae and Prof. Fleming have studied the electrical resistance 

 of metals at the temperature of boiling oxygen, —197° C, and 

 find an enormous decrease in the specific resistance of perfectly 

 pure metals. Pure iron at —197° C. has ■£$ of its resist- 

 ance at 100° C. and pure copper -^ T . The smallest impurity 

 affects the results to a remarkable degree. A carbon filament 

 such as is used in an incandescent lamp continually increased in 

 resistance as the temperature was lowered. Carbon thus acts 

 just the reverse of metals. Iron and nickel change most. Pure 

 iron at the temperature of boiling oxygen, — 197° C, conducts 

 better than electrolytic copper at ordinary temperatures. — Phil. 

 Mag., Oct., 1892, pp. 326-337. J. t. 



II. Geology and Natural History. 



1. Les Regions Invisibles clu Globe et des JEspaces celestes: 

 JEaux Souterraines, Tremblements de Terre, Meteorites / par A. 

 Daubeee, Membre del' Institut. 240pp. 8vo. 1892. — This volume 

 is one of the series entitled "Bibliotheque Scientifique Interna- 

 tionale," published at Paris under the direction of Em. Alglave. 

 Prof. Daubree has here brought together some of his very valu- 

 able papers illustrating geological principles by experimental re- 

 searches. The papers included are the following : I. The work 

 of subterranean waters at the present time; II. The part they 

 have taken as mineralizers during geological time ; III. Earth- 



