Page:Popular Science Monthly Volume 92.djvu/291

 Popular Science Monthly

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��shaft at the center of the switch to move in either direction and to break the cur- rent circuit by contacting with one or the other of the two bell-crank levers. The two movable rubber blocks on which the bell-crank levers are mounted, are ad- justed by screws, work- ing in the slots shown, so that the contact on the right opens when the curtains have reached their upper limiting positions, and that on the left when they have reached their lower limiting positions.

The system has a number of defects, due mainly to the fact that it was not in- stalled until after the walls of the lecture room had been started. This made it neces- sary to operate the curtains entirely from the tops of the win- dows. It would be more satisfactory if the curtains could be operated from below rather than from above. This would allow them to be pulled down by the motor and then roll them- selves up through the action of the roller spring, the pawl being removed to allow free action.

Wood Flour Is a New Pro- duct Made from Sawdust

WOOD flour is made by grinding dry sawdust in the same way that grain was formerly ground in the old- fashioned mills. At the pres- ent time it is used in ammu- nition plants as an absorbent in preparing dynamite. Chemically-bleached wood flour is used in making wood stucco and molding. In fact, wood flour is coming into wider commercial use each day.

���A brief case converted into a knapsack for holding an engineer's blueprints

��A Lawyer's Brief Case Is the Engineer's Knapsack

IF soldiers use knapsacks, why not en- gineers? So thought a railroad en- gineer and he straight- way devised the knap- sack shown. A strap is attached to an or- dinary brief case and goes over the wearer's shoulders. As many as a dozen blueprints can be folded and tucked into the pock- ets of the case. Two straps are sewed on the back to serve as holders for rolled-up drawings that are too big to go into the case sections. For carrying his drawing instruments another pocket is placed just above the two straps. In this way, the engi- neer can carry supplies along and yet have his hands free.

��Here Is a New Tool for Grinding Your Automobile Engine Valves

THIS new type of valve grinder differs from others which you have seen. While the handle is turned in one direction only, the shank that turns the valve is re- volved alternately in op- posite directions to produce the forward and backward action so necessary for per- fect valve grinding. This unusual action is secured through the use of two gears with segmental teetn, which alter- nately come into contact with a third horizontal gear on the top of the verti- cal shank of the de- vice, as shown in the illustration.

���Though the handle is revolved in one direction only, the grinder part reverses itself

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