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.
(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.
