162 



Scientific Intelligence. 



which would rotate about a magnet — the earth. By unipolar in- 

 duction electromotive forces must be set up which would drive 

 the electricity in the higher atmosphere from the equator to the 

 pole. The auroras boreales and the daily variations of terrestrial 

 magnetism would be referred to these phenomena. — Phil. Mag., 

 July, 1889. — Meteor. Zeitschrift, v, 297, 1888. . j. x. 



8. Disruptive discharges in gases. — M. Wolf concludes from 

 his investigations that : 



(1) The electrical force required for disruptive discharge in dif- 

 ferent gases, between spheres of 5 cm. radius at a distance of 

 0*1 cm., increases with the pressure of the gas between 1 and 9 

 atmospheres. 



(2) The increase of electrical force for an increase of pressure up 

 to one atmosphere is for simple gases, oxygen, hydrogen, nitro- 

 gen and atmospheric air, inversely proportional to the mean 

 wave-length of the gas molecule. 



(3) With carbonic acid gas the product of the increase of elec- 

 trical force, for one atmosphere increase of pressure, into the mean 

 wave-length is noticeably smaller (about one-half) than with sim- 

 ple gases. 



(4) One or more discharges are needed before the normal resist- 

 ance of the gas is reached. The resistance also is smaller in 

 comparison with that of later discharges the higher the pressure 

 of the gas. — Ann. der Physik und Ghemie, No. 6, 1889, pp. 306- 

 315. j. t. 



9. Selective reflection of Metals. — H. Rubens has carried out 

 at Strassburg and in Berlin under Kundt a research upon this sub- 

 ject. The apparatus consisted of a spectroscope, the eye-piece 

 of which was replaced by a bolometer. By a mechanical arrange- 

 ment a standard lamp could replace the metallic mirrors from 

 which the light was reflected, and thus a comparison could be 

 made, the lamp being placed in the position of its virtual image. 

 The ratio of the heat measures gave the selective absorption of 

 the mirror under examination for the. wave-length A. 



The following table exhibits the results : 





Silver. 



Gold. 



Copper. 



Iron. 



Nickel. 



0-45 fi 



87-0 



43-4 



53-0 



58-7 



61-7 



0-50 " 



88-3 



56-1 



54-8 



57-7 



61-0 



0-55 " 



90-3 



71-1 



70-0 



56-1 



62-1 



0-60 " 



927 



80-5 



77-7 



57-6 



63-4 



0-65 " 



93 '3 



85-3 



80-7 



59-6 



65-8 



0*70 " 



94-5 



90-3 



83-3 



61-4 



67-8 



0-80 " 



95-2 



92-4 



85-4 



63-6 



70-4 



0-90 " 



95-8 



95-2 



87-3 



64-7 



73-1 



1-00 " 



96-5 



96-8 



88-9 



69-0 



77-4 



1-15 " 



97-0 



97-3 



89-5 



72-3 



80-4 



1-40 " 



97-4 . 



97-0 



91-3 



74-3 



81-7 



1-65 " 



97-7 



97-0 



93-0 



78-4 



83-9 



2-00 " 



97-3 



95-4 



93-9 



80-5 



84-5 



2-3 to 2-7 fi 



97-0 



89-0 



95-0 



86-6 



88-0 



2-7 to 3-2" 



98-3 



84-2 



96'4 



89-6 



91-7 



-Ann. der Physik und Ghemie, No. 6, 1889, pp. 249-268. J. t. 



