710 



SCIENCE 



[N. S. Vol. XL. No. 1037 



ting a beam of light to enter a dark room and 

 fall upon the face of a diamond such as used 

 in rings. The diamond is held a few inches 

 from the hole through which the beam of light 

 enters and upon this screen is thrown a large 

 number of bright spots very closely resembling 

 the X-ray patterns. By moving the diamond 

 to and fro from the screen or by rotating it 

 the form of the pattern can be altered. The 

 portions of rays that enter the diamond and 

 are reflected from the rear surfaces may show 

 the spectral colors. 



This experiment can be demonstrated to a 

 class very easily and should be of some use in 

 explaining crystalline structure. 



W. W. Strong 

 The Carnegie Institute op Technology, 

 Pittsburgh, Pa. 



a new method of preparing spiders for ex- 

 hibition in museum groups 



The preservation of spiders for museum 

 purposes has always presented serious diffi- 

 culties on account of the fact that the ab- 

 domens of the Arachnids lose their shape and 

 color on drying. The usual method of preser- 

 vation in liquids is of course out of the ques- 

 tion when spiders are to be used as part of a 

 faunal group. By preparing an artificial ab- 

 domen of wood and fastening it to the cephalo- 

 thorax of the actual specimen I have found it 

 possible to produce an imitation which can 

 scarcely be distinguished from the living ani- 

 mal. 



A large number of specimens of the desired 

 species must be collected, to allow for the se- 

 lection of full-grown animals. It is advisable 

 to keep them alive for several days and to sup- 

 ply them with plenty of food; as it often hap- 

 pens that either conditions of the weather do 

 not allow an ample food supply or else the in- 

 sect may be abnormal on account of a recent 

 or impending molt. In such instances the 

 abdomen may often be not quite half the size 

 of that of a well-fed specimen or one filled 

 with eggs. 



After the insect body is fully developed, the 

 imitation abdomen must be made before kill- 

 ing. For this purpose a piece of light soft 



wood is used, carved in the exact form and 

 size. Then the coloration is put on in precise 

 shade and pattern. 



Next the spider is killed. The best way to 

 kill it is by putting it in a corked bottle con- 

 taining cyanide. According to the strength 

 of the cyanide and the size of the spider this 

 takes from one to two hours. If the length of 

 time is not sufficient the spider may later re- 

 cover. After being sure that the spider is dead 

 an insect pin is driven through the center of 

 the cephalothorax and the insect fastened into 

 a cork sheet, the legs being put in position 

 and supported with pins. After being pre- 

 pared in this manner, the insect must be kept 

 in a warm and dry place, protected from dust. 



After a few days, when the insect is thor- 

 oughly dry, the shrunken abdomen may be 

 carefully removed and replaced by the wooden 

 model. Ignaz Matausch 



American Museum of 

 Natural History, 

 New York 



SCIENTIFIC BOOKS 

 Igneous Rocks and Their Origin. By Regi- 

 nald Aldworth Daly, Sturgis-Hooper Pro- 

 fessor of Geology, Harvard University. 

 New York and London, McGraw-Hill Book 

 Company, Inc., 1914. 



In a previous publication Professor Daly 

 expressed the opinion that " to be more pro- 

 ductive geology should be more speculative." 

 In this sense the author has become highly 

 productive. In the introduction to his book 

 on " Igneous Bocks and Their Origin," which 

 is an elaboration of his previous publications, 

 he qualifies the estimate commonly put on the 

 value of experimental research in physics and 

 chemistry by remarking that, while the mathe- 

 matical methods employed are precise the 

 premises relied on are not. How much lower 

 value then must be placed on the results of a 

 procedure in which both the premises and the 

 mode of reasoning are seriously at fault! 



The author pays a just tribute to the effec- 

 tiveness of a regulated imagination, but fails 

 to warn the student of the havoc which may be 

 wrought by a badly regulated one, which like a 

 defective aeroplane may bring destruction not 



