Popular Science MonfJib/ 



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duced which mixed equally with alcohol 

 and with oils. Eventually the rat was 

 converted into pure benzol in order to 

 get rid of the alcohol. At any given stage 

 he was filled with some liquid to prevent 

 him from collapsing. Finally an air 

 pump was used. He passed through a 

 vacuum into the liquid with the same 

 index of refraction as his own. The 

 vessel containing the liquid was then 

 sealed. 



It is of course impossible to obtain 

 absolute transparency. The different 

 parts of an animal's body have different 

 indices of refraction. But it is possible 

 to make certain groups of muscles dis- 

 appear if their index of refraction is known. 

 A mixture of three parts of salicylic 

 methyl ester and one part of benzyl-ben- 

 zoate is a liquid which has an index of 

 refraction corresponding with that of 

 most animal tissues. According to Pro- 

 fessor Spalteholz, human bone can be re- 

 vealed by using five parts of oil of winter- 

 green and three of benzyl-benzoate: 



The Weight of This Dumbbell 

 Can Be Changed 



FEELING particularly strong and 

 vigorous this morning? — Add an- 

 other pound or two to each of your dumb- 

 bells. You can easily and quickly do that 

 if you own a set of the variable weight 

 dumbbells recently invented. As may 

 be seen in the diagram, each end v%eight 

 is rounded and attached to the handle 

 section by a long machine bolt with coun- 

 ter-sunk head. By unscrewing the head 

 sufficiently it is made possible 

 to insert one, two or more 

 extra weight-disks be- 

 tween each end piece 

 and the handle section. 

 The extra weights are 

 slotted so that they 

 may be slipped into 

 place without entirely 

 removing the end- 

 piece and screw- bolt. 

 After the bolt screw has 

 been tightened the 

 curved flange holds them 

 so that they cannot slip. 

 Now all you athletes, 

 go ahead and rival San- xhis dumbb^ 



dow. to suit the " 



A new hoeing machine which imitates 

 well the strokes of the human arm 



It Does the Work of Four Men — 

 This Hoeing Machine 



A HOEING machine, invented by 

 Otto F. Ullman of Severy, Kansas, 

 operates several hoe-blades simultane- 

 ously. It does the work of three or four 

 men armed with hand-hoes. Only one 

 man operates the machine. 



The hoe-blades are fixed to the lower 

 ends of arms suspended from a crank- 

 shaft. Bars extending from the hoe arms 

 to rocker arms at the rear of the machine 

 regulate the movement of the 

 hoes, imitating the strokes 

 and motions of an ordi- 

 nary hoe worked by hand. 

 The crank-shaft that 

 drives the hoe-blades 

 is connected by a 

 chain, sprocket- 

 wheels, a gear-shaft 

 and gears with the 

 main or driving axle. 

 The device may also 

 be arranged to be 

 driven by power 

 from a small gaso- 

 ing engine, but it is 

 11 can be adjusted "o^ very hard to 



pep " of the user run by hand. 



