No. 159. Moose Lake, Minn., Oct. 26, 1906.

Can a Ruhmkoff induction coil be used with a jump-spark gasoline engine with good results, and what should be the rated spark far a small 3-h. p. engine.

C. A. J

This inquiry is quite fully answered elsewhere in this issue, in the chapter on " Gasoline Engines." The ordinary coil sold for sparking purposes for jump spark ignition should give a fat spark of from 3/8 to 1/2 in. long when operated with four new dry cells of battery.

No. 160. Asheboro, N. C, Oct. 9, 1906.

Is gasoline vapor lighter or heavier than air? Where should the igniter be placed on a vertical gasoline engine. Does the charge of air and gas have to be taken into the cylinder of an engine before it will gnite.

W. C. A

Gasoline vapor is heavier thon air. Because of this fact the ventilation of boats and shops having engines using this fuel must be carefully attended to. A leaky feed pipe In a boat or building will allow an explosive vapor to accumulate in any enclosed place, and when the odor of such vapor is noticed, no flame should be allowed in the neighbrhood until after a strong current of air has circulated long enough to ensure the absence of danger.

Read the chapters recently published on " Gasoline Engines " for information about igniters.

The power of a gas engine is largely dependent upon the compression of the explosive vapor previous to ignition. Without compression, no useful work could be obtained from an ordinary gas or gasoline engine. Toy gas engines are made which, withont compressing the charge, revolve at a high speed, but develop little or no power.

No. 161. Belmont, Mass, Oct. 23, 1906.

Will you please give the B. & S. gauge numbers for the primary and secondary wire for the 1 1/2 and 3 in. spark coils described in the October, 1905 number.

I have a standard pony relay wound to a resistance 20 ohms. Would it be suitable for wireless work if rewound for a higher resistance?

What size of wire would be required to give a resistance of about 100 or 125 ohms? J. H. P.

For the primary winding of a 1 1/2 in. spark coil, the No. 16 B. W. G. may be replaced with No. 14 B. & S. G., and for the 3 in. coil the No. 14 B. W. G. with No. 12 B. & S. gauge, these numbers being sufficiently approximate to answer. For the secondary winding use No. 36 B. & S. gauge for general eqperimentnl work, and No. 34 gauge for a coil for wireless work, using about one-quarter more wire and making a larger coil in the latter case.

A " standard " relay is a full size instrument; a pony relay is smaller. Fifty feet of No. 36 copper wire gives 20 ohms resistance, which would have to be replaced with 200 ft. of the same gauge to give 100 ohms or 250 ft. to give 120 ohms. This is the- quantity for both coils of the relay, each coil having one-half the wire. No. 38 gauge has 1 ohm resistance for each l 2/8- ft. It will probably be necessary to use single silk covered wire to rewind to the higher resistance, owing to the limited space.

No. 162. Marion, III.,Nov. 13, 1906.

With an air wire, the top above all obstructions, and using a coherer receiver and a 1-inch spark coil, will a wireless outfit work about 6 miles?

Where can I buy the platinum wire sealed in a tube, as described in the June, '06 number, for use in wireless telegraphy?

Will a 2-inch spark coil operate an X-ray tube successfully? O. L.

The statement has been repeatedly made in this column that no reliable estimate can be made of the distance a wireless outfit will operate successfully. The conditions vary so greatly that actual tests are necessary to determine the capacity and power of such instruments. It is extremely doubtful if the sizes of the instruments you give, have sufficient capacity for even half the distance you state.

You will leave to make up the receiver described in the June, '06, number.

A coil giving a fat 4-inch spark in about the smallest that can used for X-ray work and even with a coil of that size the tube must be a small one. A 6 or 8-inch spark coil is ordinarily used. A 4-inch coil in series with a Tesla coil, will give much better results than the 4-inch eoil alone.

No. 163. Mosgrove, Pa., Nov. 20, 1906

Will you please advise me if there is any danger of lightning coming in over an " aerial " wire of a wireless telegraph outfit and damaging the instruments.

L. O. H. Every aerial wire should be fitted with a lightning arrester and ground as described in the Nov. '05 number of this magazine. If not so protected the instruments, even if any trace of them could be found after a "burn out " by lightning, would be of no value.

No. 164. Carmine, Tex. Nov. 16, 1906.

How many feet and what gauge wire is used in winding a 20-ohm telegraph sounder?

How many dry batteries should be used to operate a 1-inch spark coil? R. A.

See answer to No. in this 161 column. Five or six dry cells should be sufficient to run a 1-inch spark coil of ordinary construction. With a suitable primary winding as many as eight cells may be used.

Blanks for nickels for coinage cost 14 cents a hundred, and blanks for cents cost 7 3-10 cents a hundred. They are sent to the mint in Philadelphia, where all minor coins are made, and each one is struck with the design that gives to it commercial standing.