A. M. Trogner

To make a simple, yet effective current detector, procure a glass tube, some No. 26 wire, two corks, nails, and wood for base. Drill a hole in the base-board large enough to insert the test tube. Make a card-board bobbin to fit over the test tube, so that when the tube is through the board and the bobbin is placed over it there will be from one to two inches of the tube clear above the bobbin, as shown in Fig. 1.

Simple Current Detector 275

Then take a cork and cut to the heart shape shown in Fig. 2, the dimensions depending upon the size of the test tube. Insert an iron nail in the cork, making sure that the cork will bear the weight of the nail when placed in water.

The next thing is the winding of the bobbin. Five layers are wound of No. 25 copper magnet wire, and then covered with shellac.

To assemble the parts, first fill the tube with water, then place it in the cork float and cork up the tube. Next invert the tube and insert it, from the bottom, in the hole in the base-board. Then place the bobbin over the tube and connect the ends of the wire to two binding posts, and the instrument is ready for use. On passing a current through the wire the cork will sink down within the bobbin. If it does not, then loosen or tighten the cork stopper, or change the direction of the current through the bobbin until it does.