468 Explanalion of an Optical Deception. 



Buckland, is related in a paper on the Habits of Animals, by 

 Mr. Broderip, in the Zoological Journal, No. V. 



Having occasion to suspect that hedgehogs, occasionally 

 at least, preyed on snakes, the Professor procured a common 

 snake [Coluber natrix) and also a hedgehog which had lived 

 in an undomesticated state some time in the Botanic garden 

 at Oxford, where it was not likely to have seen snakes, and 

 put the animals into a box together. The hedgehog was rolled 

 up at their first meeting : but the snake was in continual mo- 

 tion, creeping round the box as if in order to make its escape. 

 Whether or not it recognised its enemy was not apparent ; it 

 did not dart from the hedgehog, but kejit creeping gently 

 round the box ; the hedgehog remained rolled up, and did not 

 appear to see the snake. The Professor then laid the hedge- 

 hog on the body of the snake, with that part of the ball where 

 the head and tail meet downwards, and touching it. The snake 

 proceeded to crawl, — the hedgehog started, opened slightly 

 — and, seeing what was under it, gave the snake a hard bite, 

 and instantly rolled itself up again. It soon opened a second 

 time, repeated the bite, then closed as if for defence ; opened 

 carefully a third time, and then inflicted a third bite, by which 

 the back of the snake was broken. This done, the hedgehog 

 stood by the snake's side, and passed the whole body of the 

 snake snccessively through its jaws, cracking it, and breaking 

 the bones at intervals of half an inch or more ; by which ope- 

 ration the snake was rendered entirely motionless. The hedge- 

 hog then placed itself at the tip of the snake's tail, and began 

 to eat upwards, as one Vvould eat a radish, v.'ithout intermission, 

 but slowly, till half of the snake was devoui'ed, when the hedge- 

 hog ceased from mere repletion. During the following night 

 the anterior half of the snake was also completely eaten up. 



EXPLANATION OF AN OPTICAL DECEPTION : BY DR. ROfiET. 



A curious optical deception takes place when a carriage- 

 wheel, rolling along the ground, is viewed through the in- 

 tervals of a series of vertical bars, such as those of a palisade, 

 or of a Venetian window-blind. Under these circumstances 

 the spokes of the wheel, instead of appearing sti aight, as they 

 would naturally do if no bars intervened, seem to have a con- 

 siderable degree of curvature. The distinctness of this appear- 

 ance is influenced by several circumstances presently to be 

 noticed ; but when every thing concurs to favour it, the illusion 

 is irresistible, and, from the difficulty of detecting its real 

 cause, is exceedingly striking. 



The degree of curvature in each spoke varies according to 

 the situation it occupies for the moment with respect to the 



perpendicular 



