Vivifying Power of Light and Heat. 1 5 1 



for a short time in the dusk of the evening when hunger 

 compels them to bestir themselves. And this view is 

 not so fanciful as it may seem to be at first sight, for it 

 is a fact that nocturnal animals, confined in menageries, 

 and fed in the daytime, sleep soundly enough through 

 the night and through the day also are, in fact, always 

 sleeping unless they are awakened by the pinches of 

 hunger. 



Whether the life of animals responds to the moon as 

 well as to the sun is a question to which as yet it is not 

 easy to return a decided answer. It is difficult to believe 

 that there is nothing in the notion that the mastiff in 

 the yard is more disposed to bark and howl in the moon- 

 light than in the dark. It is difficult to believe that 

 there is nothing in the Indian notion that wild animals 

 " observe the feast of the full moon " by imitating the 

 noisy behaviour of the yard-dog when he " bays the 

 moon " a notion of which so vivid an account is given 

 by Humboldt in one of the chapters of his ''Aspects of 

 Nature." It is difficult to believe that there is nothing 

 in the old notion that the full moon is in a measure to 

 be blamed for exacerbations of lunacy, and that the 

 persons so affected are rightly called lunatics. And 

 certainly these difficulties are not lessened when the 

 attention is directed to those physiological changes in 

 the human frame in which a monthly, and therefore a 

 lunar, cycle, is more clearly perceptible than in any 

 merely pathological changes. In fact, it can scarcely be 

 doubted that there are tidal movements in animal life in 

 which the conjoined action of the sun and moon would 

 be plainly enough perceptible if the example set by Dr. 

 Mead, and put on record in his treatise, " De imperio 

 solis ac lunae in corpora humana et morbis inde oriundis," 

 were more frequently followed. 



