Page:Popular Science Monthly Volume 89.djvu/462

 448

��Popular Science Monthly

��A New Variable Condenser

��MOST experimenters find difficulty in constructing \'ariiible condensers such as sold on the market, in which the effectiw area of the plates varies. In the condenser here described, the distance between the plates is varied.

The instrument is mounted on a circular base 5K ins. in diameter; A and B are brass disks 2}4 ins. in diameter; B is soldered to screw E and fastened to the base as in the drawing. A wire from E connects B with a binding-post; C and C are rubber pillars upon which the brass rod D is mounted. The rod is threaded so that A will remain parallel to B. Between the two disks, insert a sheet of mica F, about .005 of an in. in thickness. The capacity is varied by turning the knob G. The maximum capacity will be .00176 mfds. with the best grade of mica. — Matt Jarosz.

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��The Distance Between the Plates in This Condenser is Variable

The Quenched Gap

AMOX(i (ither things the close coup- L ling, and consequently the increased etiicieiicy of radiation, possible with this type of gap, make its use \ery desirable. Unfortunately it does not prove very satisf.utory for amateur use, as the 60-cycle current usually sui)plie(l on lighting circuits to which amateurs have access, used with ordinary trans- formers, often gives a very mushy note to the spark. This renders it unsuitable for working through static or other interference. The difhcully ma\' be avoidi-d to some e.xlent 1)>' using (he i|Uenched ga[) in si-rie^ with a rotary gap, thus raising and regulating the frequency of the discharges. The

��quenched gap can al.so be u.sed with a spark-coil, but the resulting note is not always very satisfactory.

With regard to the adjustment of the gap, it should be noted that the plates must be kept clean and air-tight.

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��A Kickback Preventer

apparatus described herein is )ne of the simplest forms of kick- back preventer, and will take care of all high frequenc>- surges on the primary leads of a wireless transformer.

It consists of three plates of aluminum, immersed in a saturated solution of sodium phosphate or bi-carbonate of soda.

In the drawing is shown a method for suspending the plates in a common quart mason-jar. The instrument is to be connected to the apparatus as shown in the wiring diagram.

Its action is not unlike that of a condenser, due to the thin in- sulating film that forms on the plates when current tries to pass from one plate to the other. Any ex- treme In* high voltage surges will puncture this film and thus be d i s - charged to earth. The fuses will prevent the flow of too much live current. The film is replaced .lutomatically when the voltage is reduced. It ma\' be noteil that two small alinninuni plates immersed in the aboN'e solution placed in a test tulu', will form .1 good renewing condenser ol fairly high capacity.— Roukkt Kicn.nkuv.

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^Aluminum PJaks

��Method of Suspend- ing the Plates in a Quart Mason Jar

���Diagram of the WirinR by Which Instruments are Connected

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