* the eastern, is the cause of the 
ce a in the tempe This inference, is not however in 
accordance with facts, as the low temperature is not proportional 
to the distance from the western coast. Throughout this part of 
the northern hemisphere, it is found that climate has certain rela’ 9 
tions to the elevation of land, not simply arising out of the ele- 
vation of that part of the earth’s surface above the general level, 
but out of the influence which the elevation exercises on the 
atmosphere. After an extensive discussion of facts, Mr. H. con- 
siders himself warranted iri concluding that the great difference 
in the winter climates of certain parts of the northern hemis- 
phere, is attributable to elevations of land intercepting and con- 
densing atmospheric steam, and thus rendering those parts wet 
and warm, while cutting off the mapphystam the more northern 
pee leaves them dry and cold. 
On the theoretical omepathtion of Refractive Indices, by. Prof. 
Powell.—In the Report on Refractive Indices, which the author 
had presented to the Association, his professed object extended only 
to exhibiting the results of observation without any reference to 
theory. Since that report was made, he has devoted his attention 
to the subject of their ¢heoretical computation, and it is the object 
of the present communication to state very briefly the progress 
made in it. ‘The results in the Report on Indices are classified’ 
under three heads: 1, those of Fraunhofer; 2, those of Rudberg; 
3, those derived from the latest observations of the author, com= 
prising many new results, superseding former ones; and others, 
the combined results of several sets of earlier observations com- 
pared with later. The first series was compared with theory, 
1, by the author in the Phil, Trans. 1835, but only by an ap- 
proximative and tentative method; 2, by Mr. Kelland, by a direct 
and exact method in the Camb. Trans. Vol. 6; 3, for the rays 
D and C only, by Sir W. R. Hamilton in the Phil. Mag., 3d 
series, Vol. 8; 4, by M. Cauchy in the Nouv. E'rerc. livr. 3-6, 
by a most exact and elaborate process. ‘The second series has 
been computed only by the author, by the same approximative 
method as the first, in the Phil. T'rans. 1836, whence it was re 
printed in Peszendorf’s Annalen. Some of the first results be- 
iy: to the third series were computed by the author, by Sit 
W. R. Hami nes in the Phil. Trans. 1837, and three 
of the h : appeared, were recom- 
* bi —_ PP 
