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.
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