m 
of the Radiation of Heat in the Atmosphere. 
unless due allowance is made for the excess of temperature, the 
velocity of the wind, length of time of exposure, &c. we cannot 
get even an approximation to the true force of solar radiation. 
But in the hot countries, much higher temperatures have 
been obtained with naked thermometers, than any yet men- 
tioned. In CafFraria, Mr Barrow saw an exposed thermometer 
mark 106°. The missionary Campbell, during his interesting 
journey in the winter time through the country of the Botchua- 
nas, when the air at 8 a. m., saw the thermometer in the sun at 
noon rise to 84°. At Gondar in Abyssinia, Mr Bruce mentions, 
113°; while at Benares, 110°, 113°, and 118° respectively, are 
recorded. There is another class of observations to which Mr 
Daniell has not alluded, though entitled to more confidence than 
those with naked thermometers. The force of the sun’s rays 
may be conveniently ascertained, by taking the temperature of 
the surface of the earth, where it has been fully exposed to the 
effects of insolation. Observations of this kind are very inte- 
resting, but they are unfortunately few in number. We shall 
here cite some of those best authenticated. 
In Sierra Leone, Dr Winterbottom saw a thermometer, placed 
on the ground, rise to 138°. Humboldt gives many instances of 
the temperatureof the earth being so high as 118°, 120°, and 129°; 
and at one] time he found the temperature of a granitic sand, 
loose and coarse-grained, 140°.5 ; another, finer and more 
dense, 126°, the thermometer in the sun being at the same time 
97M6. “ It is probable,” he .observes, “ that the mean tem- 
perature of the dried mud, in which the alligators bury them- 
selves during their state of periodical lethargy, is more than 104° 
Fahr.”; that is to say, at least equal to the mean of maximum 
temperatures registered by Mr DanielPs black thermometer. 
Now, the mean of all his observations on solar radiation, including 
the summer of 1 822, is only 79°.4. Fahr. We do not recollect any 
observations of this kind in our latitudes, except that mentioned 
above, where the temperature of the slates was 119°. Mr Cold- 
stream informs us, that, on a very hot day in June last year, 
he found the temperature of the surface of an oil-painted garden 
seat, in a sheltered spot, with the sun beating upon it, to be 
l 
