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Monday , 7 th March 1859. 
Professor KELLAND, Vice-President, in the Chair. 
The following Communications were read : — 
1. Some Inquiries concerning Terrestrial Temperature. By 
Professor J. D. Forbes. 
In this paper the writer starts by assuming Dove’s Tempera- 
tures for the mean of every 10th parallel of latitude, from 75° N. 
to 40° S., to be correct. His object is to inquire how far the influ- 
ence of the proportion of land and water in modifying the annual 
temperature of a given parallel is susceptible of being reduced to a 
formula. 
The amount of land and water in different latitudes is first tabulated. 
It is then shown, from an examination of the ordinary isothermal 
curves, and also from Dove’s charts of the “ Thermic Anomaly,” 
that the influence of land is to exalt the temperature of lower lati- 
tudes, and to depress that of higher latitudes. About the latitude 
of 42 °or 43° this influence is nil ; and the temperature of that 
parallel is independent of the proportions of land and water. For 
convenience of calculation, however, the latitude of 45° is assumed 
as the one free from this anomaly. 
The writer shows that the decrement of temperature along an 
oceanic meridian (that of Greenwich, for example) proceeds nearly 
as the simple cosine of the latitude (which is Sir D. Brewster’s for- 
mula) ; while along a continental meridian (one passing through 
Siberia) it is more nearly as the square of the cosine (the law of 
Mayer.) 
Hence it is argued that the temperature of any parallel may pro- 
bably be represented by a formula containing (1) a constant ; (2) 
a term varying with a power of the cosine not differing much from 
unity ; (3) a term for the effect of land, containing as a factor the 
proportion of land on the parallel, and also the factor cos. 2 lat,, 
which renders it additive below 45°, and subtractive afterwards. 
VOL. IV. 
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