gy and Natural History. 317 



ticularly of the absorption of the sun's radiation by carbonic acid 

 in the earth's atmosphere. The results of Langley arc oommented 

 upon, ami compared with the author's results. A formula is found 



which expresses the results fairly well. If i represents the heat 

 passing through an atmospheric Layer of thickness </, then i = A, 



in which A, and /) i represent weak and A, and p, 

 strong carbonic acid absorption, /J, can be taken as the mean 

 value o\' Langley's coefficient. A very satisfactory agreement is 



found between the calculated and observed values. To carbonic 

 acid absorption the author attributes the sharp rise in the intens- 

 ity of radiation with high altitude of sun, which Langley's coeffi- 

 cient does not fully express. — Ann* der Physik tend Uhemie, 1890, 

 X... J; pp. 2(37-311. J. t. 



!>. Method of rotating mirror. — A. v. Oettingen believes 

 that a plane mirror before a stationary photographic objec- 

 tive is to be preferred to the method of a rotating concave 

 mirror. The images are sharper and there is greater range in the 

 disposition of the apparatus. — CentiraUstgf Opt. u. Mech., 8, 1887. 

 BeibUUU /• Ann. der Physik und (Jhem., L890, No. 1, p. 33. j. t. 



Thermo- Electricity. — Dr. DeCoudres, of Leipzig, lias suc- 

 ded in detecting a thermo-electric tension between compressed 

 and uncompressed mercury. The compression was produced 

 either hydraulic-ally or by means of its own weight acting through 

 a column of mercury. It was found possible to determine with 

 certainty the direction of the thermo-electric current, and to 

 measure its intensity for given pressures and temperatures. — 

 Nature, Feb. 2 7, 1890. j. t. 



11. Measurement of Electrical resistances. — At a meeting of 

 t^e Physical Society of Berlin, Feb. 7, Dr. Fetjssner spoke of the 

 methods adopted at the Government Physico-Technical Institute 

 for the measurement of electrical resistances. The wires are 

 wound upon metallic cylinders in order to provide for the rapid 

 cooling of the wires as they are warmed by the passage of the 

 current ; these are then submerged in petroleum, whose tempera- 

 ture is recorded by a thermometer immersed in the liquid, which 

 is itself kept constantly stirred. German silver wires are unsuit- 

 able for standard resistances, since their resistance increases with 

 lapse of time. This tendency was attributed to a gradual crystal- 

 lization due to the zinc in the alloy. Wires made of an alloy of 

 copper and nickel have been examined.. Wires made of this alloy 

 possess a very low temperature coefficient, and were found to be 

 very constant after being heated to 100° C. — Nature, Feb. 27, 

 1890, p. 40 7. j. t. 



II Geology and Natural History. 



1. Subaerial decay of rocks and Origin of the Red color of 

 certain formations; by I. C. Russell. Bull. U. S. Geol. Survey, 

 No. 52. — In this paper Mr. Russell treats at length of the amount 

 of decay over the middle and southern parts of the Appalachian 

 border of the United States, dwelling on its extent, its relation to 



