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THE POPULAR SCIENCE MONTHLY 



lated, that I should have been quite de- 

 ceived, had I not seen that the fly was still 

 upon the window. Accordingly I drew his 

 attention to this fact, as well as to the ab- 

 sence of any thing upon the floor; and, 

 when he saw that his hypocrisy had been 

 detected, he slunk away under some furni- 

 ture, evidently very much ashamed of him- 

 eelf" 



Mecbaukal Action of Light. It has been 

 supposed that the rays of light, as distin- 

 guished from heat-rays, can produce no 

 mechanical effects, such as repulsion and 

 attraction ; and the circumstance that these 

 rays are unable to propel the arms of a vane 

 suspended in vacuo has even been employed 

 as an argument against the truth of New- 

 ton's emission theory of light. Mr. William 

 Crookes, however, at a recent meeting of 

 the London Royal Society, exhibited an ap- 

 paratus which he calls " the radiometer," 

 by means of which he proves that the 

 luminous rays produce direct mechanical 

 effects, after all the thermic rays have been 

 strained out. The radiometer is described 

 as consisting of four pith disks, fixed at the 

 extremities of two crossed arms of straw 

 balanced on a pivot at the point where the 

 straws cross each other, so that they can 

 spin round on the pivot. These pith disks 

 are white on one of their sides and black- 

 ened on the other. The entire arrangement 

 is inclosed in a glass bulb, from which the 

 air is removed by means of a Sprengel 

 pump. On being subjected to the action 

 of light from which ninety-five per cent, of 

 the heating rays had been strained out by 

 means of an interposed plate of alum, the 

 disks rotated with a speed little inferior to 

 that when the heat-rays were allowed to 

 mingle with the rays of light. And what 

 is very singular, it is the blackened surface 

 which is repelled by the luminous rays. 

 Inasmuch as light is reflected by a white 

 surface, and absorbed by a black, one 

 should expect that in the experiment the 

 white faces of the disks would rather be re- 

 pelled. This anomaly Mr. Crookes does 

 not attempt to account for, and he is con- 

 tent to let the facts speak for themselves, 

 being confident that in due time the laws 

 governing them will be made manifest. 



It having been suggested by Prof. Os- 



borne Reynolds that the movement of the 

 little vane might be due to evaporation and 

 condensation on the surface of the pith 

 disks, Mr. Crookes showed that this was 

 not the ca.se. He exhibited the very same 

 effects with a lever-arm of platinum, sus- 

 pended by an arm of platinum, the whole 

 of which had been heated to redness again 

 and again, during thirty-six hours of ex- 

 haustion by the Sprengel pump. 



Prof. Dnxley on the Amphioxns. In 



a preliminary note upon the brain and 

 skull of Araphioxus (the lancelet), Prof. 

 Huxley shows that, although these organs 

 are not fully differentiated in this animal, 

 yet well-marked divisions of the nervous 

 axis and spinal column exist which answer 

 to the encephalon and cranium of the higher 

 fishes. The homologies of the anterior pairs 

 of nerves are worked out, and the skull is 

 considered to be represented by the seg- 

 ments of the body which lie in front of the 

 fifteenth, counting from before backward. 

 The many points of resemblance in struct- 

 ure between the lancelet and the young 

 form or larva of the lamprey {petromyzon) 

 are insisted on, and it is suggested that 

 Amphioxus should be regarded as the type 

 of a new primary division of the class 

 Pisces, to be called Entomocrania, as con- 

 trasted with all other known fishes, in 

 which the primary cranial segmentation is 

 lost, and for which the term Holocrania is 

 proposed. 



What Savages think of Twins. In 



Africa, according to Dr. Robert Brown 

 ("Races of Mankind"), the birth of twins 

 is commonly regarded as an evil omen. No 

 one, except the twins themselves and their 

 nearest relatives, is allowed to enter the 

 hut in which they first saw the light. The 

 children are not allowed to play with other 

 children, and even the utensils of the hut 

 are not permitted to be used by any one 

 else. The mother is not allowed to talk to 

 any one not belonging to her own family. 

 If the children both live till the end of the 

 sixth year, it is supposed that Nature has 

 accommodated herself to their existence, 

 and they are thenceforth admitted to as- 

 sociation with their fellows. Nor is this 

 abomination of twin births restricted to 



