INTRODUCTION. XXXV 



prove the contrary position. No person in the least acquainted with meteoro- 

 logical science will assert that the snmmer of St. Petersburgh is hotter than that 

 of Paris, or even so warm ; or that the same season at Paris exceeds in heat, whilst 

 it lasts, that of Rome, Madrid, or other cities of Southern Europe, which, if the 

 before-mentioned theory were correct, it ought assuredly to do. T am inclined 

 to attribute this popular fallacy respecting the summer of northern latitudes to 

 the effect upon the frame of a really moderate but occasionally high tempera- 

 ture, sustained through days of almost wearisome length, alternating with nights 

 so short and lucid as to invite rather to active exertion from their comparative 

 coolness, than to that quiet and repose which we instinctively seek and are 

 most fitted to enjoy during the temporary absence of light that attends the 

 earth's diurnal revolutions in regions nearer the equator. In these high paral- 

 lels the air has no time to cool considerably, or darkness to overspread the face 

 of Nature, before the sun again emerges above the horizon to dispel the faint 

 approaches of obscurity, and renew the little heat already lost by ter- 

 restrial radiation. The system is excited by the unremitting stimulus of two 

 powerful agents, whereby an impression is conveyed to the feelings, of a degree 

 of heat, which the thermometer, if consulted, would show they had greatly 

 exaggerated. The human body is here under circumstances of excitement, 

 from the continuous, rather than the intense, action of colour and light, the 

 effect of the joint agency of which on plants is to hasten their progress to ma- 

 turity, as soon as, or even sooner than, either could accomplish that end by an 

 augmented but less constantly sustained force. 



