Page:Popular Science Monthly Volume 88.djvu/311

 Popular Science Monthly

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��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.

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����When the motor is placed upon metal it will operate; on wood, it refuses to move

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