394 Mr. G. W. Walker. The Application of the Kinetic 



Length of ? 4 to 4 '5 mm. ; of $ 3'5 mm. 



Habitat. South America and India generally. 



Observations. I can see no difference between the Indian and South 

 American specimens. The insect is very marked, and can at once be 

 told by its densely-scaled dark mottled wings and leg tufts. 



Genus Uranotcenia. (Arribalzaga.) 



' Dipt. Argentina,' p. 63 (1891), Arribalzaga ; ' Mono. Culicid.,' ii, 

 p. 241 (1901), Theobald. 



Told from other Aedes by the presence of flat scales on the meso- 

 thorax and scutellum, swollen mid femora, and by the very small fork- 

 cells. A single species represented by two <^'s has been found in 

 India. 



Uranotcenia minima. (Theobald.) 

 ' Mono. Culicid.,' ii, p. 262 (1901). 



Thorax deep brown (denuded), with long black bristles ; metanotum 

 with a pale median line. Abdomen dark brown, with narrow basal 

 bands of pale yellowish-brown ; pleurae and coxoe very pallid. 



Length. 1*8 to 2 mm. (^). 



Habitat. Quilon, South India. 



Observations. I have only seen two <^'s of this species, both 

 denuded of scales. They are, however, I feel certain, Uranotcenia}, but 

 the fork-cells are a little longer than usual in this genus. 



" The Application of the Kinetic Theory of Gases to the Electric,. 

 Magnetic, and Optical Properties of Diatomic Gases." By 

 GEORGE W. WALKER, B.A. Communicated by Professor 

 PtUCKER, Sec. E.S. Received January 23, Piead February 14, 

 1901. 



(Extended Abstract. Received January 6, 1902.) 



In this paper I have endeavoured to examine the most important 

 magnetic, electric, and optical properties ef a gas, supposed to consist 

 primarily of two-atom molecules. A two- atom molecule, in which the 

 atoms are of unequal mass and carry equal and opposite electrical 

 charges, was selected not as an actual representation of the molecule, 

 but as typical of the characteristic features. I have adopted Boltz- 

 mann's distribution law, and, as far as I can judge, have not applied it 

 beyond the limits to which it appears to be justified experimentally. 



We have first to observe that the molecules may be divided into 

 three classes, which I have called A, B, and C. 



