242 Dr Richardson's Observations on Solar Eadiation, 



up the hourly columns of each month, that the curves of tem- 

 perature were very irregular, the irregularities being evidently 

 caused by the black-bulb thermometer not being properly 

 sheltered from the wind.* I have included these months in 

 the following tables, but they must be considered as very im- 

 perfect. In the winter there were many calm days, but as 

 the spring advanced the air was seldom still when the sun 

 shone; and in May, therefore, I completely sheltered the black- 

 ened thermometer by enclosing it in a large thin glass bottle. 

 In this month the mean excess of the temperature indicated 

 by the blackened thermometer over one in the shade rises in 

 the morning at each successive hour of observation, attains its 

 maximum at noon, and descends again in the afternoon, as 

 shewn in the accompanying plate (Plate V.) And this I regret to 

 say is the only month for which I possess hourly observations to 

 be depended upon. I left the Fort in June, and though Mr 

 Dease kindly continued the observations every third hour in 

 July and August, yet as he had no watch whereby to measure 

 the time, the results for these months must be somewhat un- 

 certain. It is satisfactory, however, to find that both the mean 

 excess and the maximum excess in these two months are 

 greater the nearer the hours are to noon. From September 

 1826 to the end of April following (1827), the observations 

 were continued at 8, 10, 11, a. m., and 1, 2, 4, p. m., and after 

 the middle of February at noon also by Sir George Back and 

 Lieutenant Kendall ; and though I have not their original re- 

 gisters to refer to, I have extracted from Franklin's appendix 

 as many of the results as the tables there given would fur- 

 nish. 



For these observations, a pair of thermometers correspond- 

 ing most nearly with each other in their scales was chosen. 

 Up to the end of April 1826, spirit-thermometers were used ; 

 in May, July, August, and 'September, mercurial ones were 

 employed ; and from November till the end of April 1827, the 

 spirit ones were resumed. They were all constructed by New- 

 man, and had spherical bulbs half an inch in diameter. The 

 thermometer exposed to the sun was prepared by coating its 



* See Franklin's Appendix above quoted, where the days on which the 

 wind affected the black-bulb thermometer are marked by an asterisk. 



