342 Sir D. Brewster on the Law of Daily Temperature. 



with the square of the cosine, I was anxious to obtain observa- 

 tions in high latitudes in order to test the accuracy of his for- 

 mula. Mr. Scoresby, to whom I made application, was 

 fortunately able to state it as the result of numerous observa- 

 tions made in different years, that the mean temperature in 

 the latitude of 78° was about 17°, from which he deduced that 

 of the Pole to be 10°. But as the mean temperature in the 

 latitude of 60° is 1 6° 92' less in the Old World than the New, 

 or in the meridian on which Mr. Scoresby approached 

 the Pole, it is obvious that the mean temperature of the Pole, 

 if deduced by the same process from the observations in the 

 Old World, would be even below zero. This result was 

 doubtless perplexing ; but the perplexity was soon removed 

 by the return of Captain Parry in 1820 from Melville Island. 

 He found the mean annual temperature of that island, in 74f ° 

 of latitude, to be -f- 1° 33' Fahr., thus confirming the result 

 which we had obtained and previously communicated to the 

 Royal Society of Edinburgh*. This extraordinary result, 

 taken in connexion with Mr. Scoresby's, suggested to us 

 the idea that the coldest part of the globe was not far from 

 Melville Island, and that there were " two points of greatest 

 cold not many degrees from the poles, and in meridians nearly 

 at right angles to that which passes through the west of Eu- 

 rope." From a comparison of a great number of mean tem- 

 peratures both in the Old and New World in high latitudes, 

 we were led to the conclusion that the two cold poles were 

 situated in 80° of north latitude, and in 95° of east and 100° 

 of west longitude f, — the mean temperature of the eastern 



* Edinburgh Transactions, vol. ix. p. 212, Feb. 1820. 

 f In my treatise on Magnetism, I have adopted for the place of the Ame- 

 rican pole 100° W. long, and 73° N. lat., and the Asiatic pole in 80° E. 

 long, and 73 N. lat., in order to represent better the observations of the 

 Arctic voyagers, and in order to adapt them to the general formula given 

 in the following note : — 



"The formulae for finding the mean temperature are as follows : — 

 Asiatic pole, mean temp. = 82 0, 8 sin D 

 American pole, mean temp. = 86 0, 3 sin D — 3^° 



The distance from the Pole, viz. D, is in the coldest meridian D = 80° — 

 lat., and in the warmest meridian cos D = cos 10° sin lat. In all inter- 

 mediate meridians we have cos D= — - — - — -. -, and tan 6 = cos M 



cos 6 



tan L, where M is the difference of longitude between the place and the 

 pole, L the co-latitude of the isothermal pole or 10°, and / the co-latitude 

 of the place. 



" In order to obtain a general formula for the whole globe, we must sup- 

 pose the temperature of both poles equal, and the cold meridians 180° 

 apart. In this case we have 



T = (t — t) (sin" 3 = sin" I') + r, 



