Popular Science Monthly 



283 



Rinsing Photographic Negatives 

 Without Running Water 



AMATEUR photographers who are 

 compelled to labor under the dif- 

 ficulties of developing prints and nega- 

 tives without the aid of running water, 



If the pail is high 

 enough, a service- 

 able spray will fall 

 upon the plates 



will find the apparatus which is shown 

 in the drawings to be of considerable 

 assistance. Water is syphoned through 

 a small tube from a pail, the tube lead- 

 ing to the center of a developing tray 

 where it is bent upwards at a right angle. 

 If the pail is elevated to a sufficient 

 height above the tray, the pressure will 

 cause a spray, which will be distributed 

 evenly over the emulsion surface. The 

 used water is syphoned from a corner 

 of the tray by another tube. 



Small Screws in Difficult Places 



DAB a bit of beeswax on the head 

 of the screw and push the point 

 of the screw-driver through the wax and 

 into the slot of the screw. The screw 

 will be held in just the right position 

 for driving home. Or again, if the 

 screws are of steel the driver may be 

 magnetized by stroking it a few times 

 with a magnet. Its insertion will then 

 become much easier. If the slot in the 

 head is very shallow, the screw will be 

 likely to slide over and stick to the 

 blade of the screw-driver. In this case, 

 use the bees-wax. 



Of course, it is evident that the hold 

 on the screw is very light and can be 



used only to drive a screw into its cor- 

 responding tap. For inserting wood 

 screws the above methods are out of the 

 question. 



A Mysterious Motor 



THE "Mysterious Motor" will puz- 

 zle any one. Not only the novice, 

 but professional electricians must do a 

 deal of thinking to decide how it runs. 



The little toy consists of an electro- 

 magnet over which is suspended a 

 four-spoked iron wheel mounted on a 

 thick wooden base. When placed upon 

 a flat metal surface the motor will run, 

 but when set upon a non-conductor it 

 will remain motionless. 



The thick base is hollowed out from 

 the bottom to make sufficient room for 

 a small flash-light battery. Four brass 

 tacks are driven into the base. From 

 one of these tacks runs a wire to the 

 thin copper brush, to which the iron 

 wheel acts as a comutator and arma- 

 ture combined. The current passes 

 through the brush into the wheel, 

 thence through the support to the coil. 

 From the coil it passes on to one pole 

 of the battery and from the opposite 

 pole to another tack. This leaves the 

 circuit broken between the two tacks, 

 when the brush is in contact with the 

 iron wheel. Consequently, when the 

 device is placed upon a conductor the 

 circuit is closed and the wheel revolves. 



The remainder of the cavity occu- 

 pied by the battery is plugged with 

 wood, and the base covered with heavy 

 blotting paper, allowing the tacks to 

 protrude. 



Much amusement may be derived 

 from the "Mysterious Motor," at a 

 party by announcing that you have a 

 motor that will gather its power from 

 the air, when placed upon any metal, 

 and then giving a demonstration. 



dfifitr&v^ 



When the motor is placed upon metal it 

 will operate; on wood, it refuses to move 



