Popular Science Monthly 



275 



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 



