338 SCIENTIFIC ILLUSTRATIONS [Sup 



Physical Forces in the Sunbeam. 



The strength of evidence appears to be in favour of consi- 

 dering light, heat, and actinism as three distinct principles or 

 powers, active in regulating the great phenomena of Nature. 

 In the sunbeam these powers are balanced against each other, 

 and thus are determined those differences of climate which are 

 not influenced by the physical conformation of the earth's 

 surface. It has been proved by well-conducted observations 

 that with variations of latitude there are variations in the 

 relations of these three principles. In the temperate regions of 

 the earth the actinic power is active ; as we advance to the 

 tropics, where heat increases, and 



" The sun shines for ever, unchangeably bright," 



the chemical power is weak. The photographic picture which 

 could be taken in London in a second or two, could not be 

 obtained within the tropics in less than a quarter of an hour. 

 It often happens, indeed, that prolonged exposure under a 

 blazing sun is insufficient to produce any chemical change. 

 Everything appears to favour the view that the distribution of 

 plants and animals on the surface of the earth is regulated by the 

 balance of physical forces in the sunbeam. In the seasons we 

 detect the same influences at work. Actinism or chemical power 

 is greatest in the spring ; as the bright light of summer advances, 

 the power of the solar rays to produce any chemical change is 

 diminished ; and as we advance to autumn, the peculiar heat- 

 rays come more evidently into action. I. L. 



Superstition the Protector of Monstrosities. 



The Natal rock-snake (Natalensis) is described by Sir Andrew 

 Smith as being gigantic in size, he having seen a skin measuring 

 twenty-five feet, although part of the tail was absent. It 

 feeds, he says, on small quadrupeds, and for some days after 

 swallowing one it remains in a torpid state, when it may be easily 

 destroyed. Of this opportunity, however, the South Africans 

 never avail themselves ; they have a horror of the reptile, but 

 believe that it has an influence over their destinies, and affirm 



