8 AN ACCOUNT OF THE EARLY ilATHEMATICAL AND 



not to be able to escape ; * * * * we may suppose 

 [therefore] that being destitute of food and air, the vital 

 functions will rennain suspended, * * * * ^jy^ ^^ 

 accident, being delivered from their imprisonment, they 

 recover from their torpid state." The answer to the ^/th 

 query relates to a subject upon which Mr. Dalton had already 

 begun to collect special information. In 1788 we find he 

 had commenced a series of experiments and observations 

 which led to the publication of his Meteorological Essat/s, in 

 1793, and hence we need not be surprised at meeting with 

 some truly philosophical reasons why the " air [feels] colder 

 about the times of sunrise and sunset than either before or 

 after." He remarks that "the temperature of the air, in 

 clear, serene weather, as determined by the thermometer, is 

 generally as follows : — The greatest cold in the twenty-four 

 hours prevails at or a little before sunrise ; from thence till 

 about two in the afternoon the heat gradually increases, and 

 afterwards gradually decreases, till next morning; — which 

 may be accounted for thus : the clear air, affording a free 

 passage for the sun's rays, like other transparent bodies, 

 receives very little heat from them. Of course, then, its heat 

 must be chiefly derived from the surface of the earth, which, 

 being acted on by the sun's rays, will constantly communicate 

 its heat to the adjacent air ; so that as the surface gradually 

 increases in heat from sunrise till sometime afternoon, and 

 then decreases in the same manner, so will the air also that is 

 near it." At the conclusion of his answer, "the ingenious 

 querist" is reminded, that if he "have frequently found it 

 colder about sunset than afterwards, he must have judged of 

 the temperature from sensation, and not from a thermo- 

 meter;" — a remark, by the way, which, independently of its 

 quiet humour, furnishes an excellent practical method of 

 disproving many a popular fallacy. The proposer of the sixth 

 query desires to be informed, " what system of philosophy 



