made at Fort Franklin in 1825, 1826, and 1827. 241 



since been contrived by Sir John Herschel for this purpose ; 

 but in the report of the Committee of Meteorology appointed 

 by the Royal Society, it is said, " As the actinometer can only 

 be observed at intervals in perfectly clear weather, additional 

 information with regard to solar radiation, of much interest, 

 though not of so precise a nature, may be obtained, by the 

 daily register of the maximum temperature of a register ther- 

 mometer, with a blackened bulb, exposed to the full action of 

 the sun's rays. It may be placed about an inch above the 

 bare soil, and screened from currents of air. The maximum 

 temperature indicated by such a thermometer, even in cloudy 

 weather, will generally be considerably above that of the air, 

 and the maxima and mean daily maxima of its indications 

 will, after a long series of observations, afford data of the 

 utmost value to the history of climates." As this recommen- 

 dation will undoubtedly be extensively acted upon by the ex- 

 pedition which has sailed to the antarctic regions, and at the 

 observatories established in connection with it, we may expect 

 to have in a few years a large body of facts recorded con- 

 cerning solar radiation in various latitudes ; and it will obvi- 

 ously facilitate the deduction of general laws therefrom to have 

 the means of comparing observations made in the southern 

 hemisphere with similar ones made in the arctic regions. With 

 this view, I have revised the original records of the Fort 

 Franklin observations, for the purpose of tabulating them 

 more fully than has been done in the appendix above men- 

 tioned, so that, in conjunction with the tables there given, the 

 most important of the results may be readily exhibited. 



When I first thought of commencing the observations in 

 question, I had no personal experience to guide me in the best 

 mode of conducting them, nor had I read of any example that 

 I could follow, further than the general recommendation to 

 travellers to observe the effect of the sun on a thermometer 

 with the bulb blackened or wrapped round with black wool. 

 My earliest trials were, therefore, of the nature of experiments, 

 and for two or three months were made only at times when 

 the sun shone brightly. In February 1826 I began to ob- 

 serve every hour that the sun was above the horizon, and con- 

 tinued to do so till the end of April, when I found, on summing 



