No. 116. Newport, R. I., Dec. 12, 1902.

I have read in the columns of Amateur Work several articles about spark coils and interrupters. I take the liberty to ask a little advice about them. I wound up a secondary coil containing one pound of No. 36 silk covered wire run through paraffine, and the primary had two layers of No. 16 wire. The secondary was tested with a magneto, and it was found to be all right. I made an interrupter like the sketch shown below (plain lever, not shown) and the best spark I could get was about 1-16 of an inch on ten dry cells in series-multiple. Both points on the vibrator were pure platinum.

I also have a small secondary winding, rated at 3/8 in. spark, but it will not work. The condenser is variable up to 14 M. F.

I have made an interrupter like the one in the November issue of Amateur Work, and it works very fast, but will not excite the secondary on the large coil. If you could suggest any method of breaking the circuit so that I could work these coils, I would be glad to have it. I can get a 1/4 in. spark out of a small coil by making and breaking with a file. My large coil is very near the dimensions given in the October number. F. E. M.

In au probability your large coil has broken down inside and is short circuiting between layers. It would be advisable to rewind your No. 36 wire on a lathe or other revolving device in 1/2 in. sections instead of in layers, as with layers a paper insulation is required between the layers of wire. Have diameter of each disc two inches, with a 1 1/8 in. hole. Separate sections 1-16 in. from each other by pasteboard discs. Put four layers of cotton cloth over the primary before placing the two windings together. Wax the cloth with hot paraffine.

The most satisfactory spark results are to be had from coils wound in sections with the proper amount of condenser, say 30 sheets of foil, size 4 x 5 in., and a vibrator 2 1/2 in. swing. You should easily get a 1/2 in. spark on six dry cells arranged in series, provided the primary is well wound with d. c. c wire, 3 layers, and the core is of soft iron wire, 2 inches longer than the secondary.

The vibrator described in the July 05 issue, (Page 223, Fig. 1) in the article, "Interruption of Primary Currents," is a very efficient one.

No. 117. Allerton, Mass., Dec. 5,1905.

Please give specifications for a simple coherer for experimental use. G. T. W.

The simplest coherer would be a glass tube about 1-16 in. bore and 4 in. long, with plugs turned from brass 1-16 in. rod. The ends of the rod should be brightened by rubbing in mercury. For filings use a silver coin, after heating them to cherry red in the fire. Separate the electrodes, 1-16 in. Fill the chamber less than one-half full.

No. 118. Columbus, Ohio, Nov. 30, 1905.

Will a spark coil giving 1 in. spark in one section of the country vary in results when operated with same battery and interrupter in another section?

Is it possible to communicate by wireless even when the tops of the two aerial wires on the poles are not within visual distance of each other? T. B. M.

Makers of coils prepare for climatic influence on coils by winding to give more than the rated spark. Coils which in the East give a 6 inch spark have been known to give out 7 inches in Denver and other Western cities. This is perhaps due to the lower atmospheric pressure, which enables the energy to penetrate to greater distance.

Have your poles extend in the air as far as possible above trolley and arc lights, and there will be very little other interference.