244 Dr Richardson's Observations on Solar Badiation, 

 gister of its indications is printed in Franklins appendix, and 

 when contrasted with the register of the one in the hottle, 

 shews the necessity of protecting the radiation thermometer 

 by glass if the observations are to be continued in windy 

 weather. 



From Tables IV. V. and VI., the daily curve of the mean 

 effect of the sun in May, July, and August, may be construct- 

 ed, and the plate on which the curves are exhibited contains 

 also the daily curve of temperature for the twenty-eight days 

 of May on which the observations were made (30° being sub- 

 tracted from the temperature at each hour). Table VII. is 

 added to shew the effect of the sun in raising the temperature 

 of the atmosphere between sunrise and one or two in the 

 afternoon, the maximum temperature at the two latter hours 

 being recorded. 



As the observations are tolerably complete only for one 

 month (May 1826), deductions from them as to the intensity 

 or to the total effect of the sun's rays in the different seasons 

 of the year would carry but little weight. I have, however, 

 in Franklin's appendix, broached an opinion, that in the high 

 northern latitudes of America, the average intensity of the 

 heat of the sun is greater in the spring months than near the 

 summer solstice, the greater clearness of the atmosphere 

 compensating for the smaller altitude of the sun. This opi- 

 nion is supported by the subjoined tables. In Table I., for 

 instance, the means of the maxima indications of the radia- 

 tion thermometer for February 1827 are nearly equal to those 

 for May 1826, though the times of observation were so much 

 more numerous in the latter month, and consequently there was 

 more chance of ascertaining the true maximum on each day ; 

 they are also considerably above those for the first sixteen days 

 of May 1827, when the observations were more frequent than 

 in February. In March and April 1827, the means exceed 

 those of February and May ; and if they do not do so also in 

 April 1826, it is to be attributed to the effect of the frequent 

 winds in that month on the unsheltered radiation thermome- 

 ter. The column containing the monthly maxima of the 

 black-bulb thermometer also leads strongly to the same con- 

 clusion ; and here the want of shelter is not so operative, as 



