84 Mr Blackadder on Circufnstances connected with the 
tended to prove, that that loss of heat which frequently occurs 
in the evening, is the effect of radiation. He seems to have pro- 
ceeded under the impression, that, in the circumstances of the 
case, evaporation could not have place ; or, if occasionally it had, 
that its effects were but transitory, and of trifling import : and 
this appears the more remarkable, when we attend to some of his 
own experiments and observations. 
Thus, on the evening of the 25th of August, he informs us, 
u 10 grains of wool, to which 3 grains of water had been added, 
having been laid on the raised board, near the thermometers ; at 
the end of 45 minutes the parcel was found to have lost 2^ grains 
of moisture, during the time that dry wool,” that is, wool to 
which no water had been added *, “ had become several degrees 
colder than the air.” It is to be regretted, that, in recounting 
this experiment, more attention was not paid to minute detail, 
such as the temperature of the water made use of, the mode in 
which it was added to the wool ; the temperature of the moist- 
ened as well as of the other parcels of wool, at the end of the 
45 minutes, and their relative temperatures, at various intervals, 
during that period. For, without paying attention to every cir- 
cumstance, even though apparently trifling, and without admit- 
ting every circumstance to have its due weight, it may truly be 
said of an experiment, that which has, with too much apparent 
justice, been said of a certain book, 66 Hie est in quo quaerit sua 
dogmata quisque ; atque in quo reperit dogmata quisque sua.” 
Again, 66 on the 7th of January,” Dr Wells informs us, 66 10 
grains of wool were placed on a sheet of pasteboard, which lay 
on the snow. At the end of 35 minutes the wool was 5° colder 
than the air, without possessing any additional weight.” But 
the evaporation of a very small quantity of moisture, from the 
surface of the wool, during the 35 minutes 1 exposure to the air, 
would be quite equal, in the given circumstances, to produce the 
observed decrement of heat. The object of this, and some other 
experiments, was to determine the occurrence of a considerable 
* Dr W. elsewhere informs us, that the wool he made use of in his experi- 
ments “ was white, moderately fine, and already imbued with a little moisture 
and he admits, that, even during his experiments, the wool might acquire some 
moisture, « from its imbibing it as a hygroscopic substance.’* 
