Popular Science Monthly 



149 



at W. The machine is now completed 

 and ready to operate. 



It is to be driven by a small motor, 

 bolted so that the spindle turns away 

 from the operator. The rider W is 

 placed at a point directly below the zero 

 on the yard stick, which should be at 

 the left end if a right-hand thread was 

 used. When the motor is started the 

 spindle revolves, the rider follows the 

 thread and moves along the threaded rod. 

 When the rider has moved a distance of 

 1 in., 32 revolutions have been made by 

 the spindle and a corresponding number 

 of turns wound upon the coil under con- 

 struction. When the rider has moved 

 the full length of the yard stick, the 

 spindle will have made 32 times 36 = 1152 

 revolutions. The rider is then replaced 

 at zero and the winding and calculations 

 continued. — H. W. Offins. 



A Homemade Electric Lantern for a 

 Dry- Battery Cell 



THIS lantern is constructed from an 

 ordinary dry-battery cell 23^^ in. 

 in diameter and 6 in. long, and a tin 

 funnel 23^ in. in diameter. The spout of 

 the funnel is removed and a small electric 

 bulb of one volt is 

 fastened into the 

 funnel as shown. 

 From a piece of 

 heavy galva- 

 nized sheet 

 iron cut a strip 

 J^ in. wide, 

 having a 

 length suffi- 

 cient to make 

 a clamp and 

 carrying han- 

 dle. Make a 

 small thumb- 

 switch of a 

 piece of 1/64 

 by M-in. 

 spring brass. 

 This should 

 be located near 



Handle attachment and 

 connections to battery 



the carrying handle. 

 An old electric bulb from an automo- 

 bile side lamp may be used, or a one- 

 volt lamp with a brass screw socket 

 and a porcelain base will answer the 

 purpose. Secure the funnel reflector to 

 the battery with a brass clamp, and when 



the battery is used up unscrew and con- 

 nect with a fresh one. This provides a 

 powerful and handy electric lantern which 

 is as easy to carry as the old barn lan- 

 tern and which is more satisfactory. — 

 P. P. Avery. 



An Easily Constructed Variable 

 Condenser of Brass and Tinfoil 



AKE a wooden roller 3 in. in diam- 

 eter and 4 in. long, as shown, 



M 



Wood roller with tinfoil half way over the 

 surface to vary the capacity of the condenser 



and mount it on a shaft, which may 

 well be of 3^ -in. brass rod. Thread 

 one end of the shaft so that a wooden 

 knob and metal pointer may be screwed 

 in place. Coat one half of the surface 

 of the cylinder with tinfoil, and solder a 

 fine wire connection from the foil to the 

 shaft. The shaft should project about 

 }/2 in. from the cylinder at one end and 

 about 1 Yz in. at the other (which carries 

 the knob and pointer), according to the 

 size of the cabinet to be used. 



Make a half-cylindrical piece of thin 

 sheet brass or copper a trifle larger than 

 the wooden cylinder, bending out support- 

 ing feet as shown. When these two 

 parts are finished, the condenser may 

 be assembled. 



When the knob is turned, more or less of 

 the tinfoil is presented to the sheet of 

 brass or copper and consequently the 

 effective capacity is varied. Connections 

 are made with the shaft and the fixed 

 sheet of tinfoil and with the brass or 

 copper shell which is around the outside 

 of the roller. — Thos. Millsbaugh. 



