No. 107. Tipton Ind., Sept. 6, 1905.

How are coherer filings made?

Is there a relay sensitive enough to operate when waves powerful enough to click in the telephone receiver enter upon a wireless receiver made of two carbon blocks and a steel needle laid across the same?

R. A. L

With a very fine file, prepare equal parts of nickel and silver filings, from U. S. coins, and placing same in an iron spoon bring to a bright heat over a gas burner or live coals. Then bruise the particles, when cold, until they are as fine as possible. Some coherer manufacturers use one part silver and two parts nickel; other use half and half. We have seen coherers with silver and antimony filings in equal parts, also iron and silver. Amateurs will find by experiment the mixture most sensitive and reliable for use with their apparatus.

No relay has been devised to operate when messages are received from any considerable distance on such a device. The telephone receiver and the human ear together form the most sensitive electrical receiver, and when once accustomed to the sounds, operators find the work as easy as reading from the sounder. The advantage of a relay would be in connection with a dot and dash recording device, with which permanent records are made on paper tape.

No. 108. Columbus, Ohio, Sept. 4, 1905.

Why is the primary core and winding of an induction coil so much longer than the secondary.

I. P. M

The most active part of a primary is near the ends, and the attraction is from the ends towards the middle, so all the lines of force pass through the secondary winding horizontally as well as vertically, thus giving a stronger saturation to the winding. There is, however, a chance of extending the core too far from the ends of the secondary, thereby increasing the im-pedence and choking the free action of the primary or saturating current. The design of a primary core and winding depends on the speed of the vibrator, the kind of primary current to be used, and the purpose for which the coil is to be used. For all ordinary purposes we believe the primary core and winding should extend at each end a distance of one-half the full diameter of the end of the secondary. As to the gauge of wire to be used in winding a primary for a small coil of less than 3 in. spark where primary battery is from 10 to 15 volts, amateur coil-makers will find more efficiency may be had with three layers or even four of No. 20 wire than in less layers of coarser wire. The old rule in coil construction was No. 16 wire, two layers. It will prove an interesting experiment for amateurs to wind their primaries with No. 20 or even No. 22 wire and note the results. The batteries will last twice as long, and the secondary spark will show the effect of an increased magnetic field. In every instance this may not prove satisfactory, but it is worth trying.

No. 109. Medford, Mass., Sept. 7, 1905.

Will a long roll of poultry netting buried in permanently moist soil answer for a wireless telegraph ground ?

Where can I buy an experimental coherer, or the parts of one ?

Has a 20-ohm sounder any advantage over a 4-ohm sounder for local work ? C. O. M.

It will answer very well until it rusts and falls to pieces.

Address any electrical dealer advertising in this paper.

No. The 4-ohm is better, as it uses less battery and makes as clear and loud sounds as any.

No. 110. Rockland, Me., Sept. 5, 1905.

Can a common magnet from a telephone be used to operate a spark coil ? If not, what changes are necessary to make one work to satisfaction ? Also, please tell me whether a magneto could be used to charge small storage cells, and what changes should be made in the magnets? H. L. D.

We are in doubt as to the meaning of the first question. Telephones are sometimes fitted with coils having primary and secondary windings, but such coils, even after being fitted with cores, vibrators and condensers, would develop only a very minute spark. The better way, if only a small coil is wanted for experimental purposes, is to make one from specifications to be found in article published in this number. A telephone magneto cannot be used for charging small storage cells, as the current therefrom is alternating, and constant current is necessary for such work.

No. 111. Huntington, Pa., Sept. 2, 1905.

Will you kindly inform me if the articles on "Amateur Runabout" are to be completed, and when? Would you advise a single cylinder engine of 5 to 7 h. p., or would a double opposed air-cooled engine of the same power be more desirable? I live in a very hilly country, and do not know whether air-cooled or water-cooled would be most efficient in climbing hills. What would you advise? H. G. C.

The articles on the " Amateur Runabout" will be continued as soon as the constructive work on the one being built has advanced enough to provide new matter. The motive power in the one being built has been changed to steam, however, as the writer was desirous of testing steam power in comparison with another of about the same size, using gas engine. Regarding type of engine best adapted for your use, if you are enough of a mechanic to be able to take care of the few additional fixtures required by the two-cylinder engine, it is the best to use in a hilly country. The best one-cylinder engines make slow work of hills, even on low speed, unless the power is large in comparison with weight of car. Air-cooled engines are doing good work in hilly countries, and any tendency to get overheated can usually be overcome with a fan run from fly-wheel or shaft.

No. 112. Larson, Wis. Aug., 30, 1905.

What size of magnet wire for primary and secondary for making a 4-in. spark coil ? Also how much of each ? Size of bobbin ? What size of spark coil for a wireless telegraph 80 rods long ? What should be the dimensions for same? How can I drill holes through plate glass? How can circular discs be cut from glass? What is the resistance for 225 ft. of No. 32 magnet wire?

Specifications for coils of various sizes are given elsewhere in this magazine. A 1/2-in. spark coil would operate for wireless work over a much greater distance than 80 rods, but as that size is easily made at small expense, would recommend it. The drilling and cutting of glass discs is fully described in the April, 1902, number of this magazine, a copy of which will be mailed you for ten cents. The resistance of 225 ft. of No. 32 magnet wire is nearly 27 ohms.

No. 113. Malden, Mass., Aug. 26, 1905.

I am about to make a wireless apparatus to operate to a friend's house about 1500 feet away. What size spark-coil would 1 need for such a line? Do I need a pole? Do the aerial wires have to be of the same height? What would be the best and cheapest receiving apparatus? Would the receiver described in the April '04 number answer? If so, please explain the wiring for that instrument, as I do not fully understand it. How many cells of battery would I need for above? E. W. P.

A coil giving 1-in. spark would probably answer, but a 2-in. spark would be better. Much depends on the nature of the ground over which messages are to be sent. If thickly settled with electric light and other electrical lines frequent, aerial terminals should be at least 75 feet from the ground, which could be secured by mounting a short pole on the roof of the house. The stronger coil would be almost a necessity. The heights and lengths of the aerials should be approximately the same. The receiving apparatus described in the April, '04, number would be a good one for first experiments, and when skill and knowledge of the local requirements had been obtained, the one in the August, '05 number could be made, the latter being much the most sensitive, but more difficult to make and operate. The receiver, or more properly wave detector, is connected in series between the aerial and ground, and the telephone hearing receiver is in shunt with same, being taken from the two center binding posts, as illustrated in the April, '04 number.

A study should be made of the different circuits shown in connection with the various articles on wireless apparatus, as published from time to time. The battery requirements for coil are dependent upon size and wiring of primary circuit, also type of battery used. If dry cells, the primary circuit should have three or four layers of No 18 or 20 wire. If accumulators, the usual winding of two layers of No. 12 to 16 wire is best.

- No. 112. So. Fkamingham, Mass., Aug. 28, '05.

I have made a spark coil for a gas engine, but cannot seem to get a spark from it. Can you give me any idea as to what is the matter with it? The coil is made as follows: Core, 7 in. long, 9-16 diameter, soft iron wire covered with heavy paper (dry.)

The primary is three layers of 103 turns each of No. 18 d. c. c. magnet wire, 1 in. outside diameter. On top of this is wound 1 lb., 15 oz., of No. 26 cotton covered magnet wire, making 203 turns and 30 layers in the length of the coil, which is 5 3-16 in. inside the ends. Between each layer of the secondary is a piece of tissue paper (dry). The outside diameter is 2| in. By dry paper I mean paper that has no coating or preparation on it. C. I. G.

Your description of the coil makes no mention of insulation between primary and secondary winding. The two should be well insulated by a pastehoard tube thoroughly soaked in paraffine or shellac. If coil has such insulation, and gave spark when first tried but no longer does so, the insulation of secondary has broken down, and secondary will have to be rewound. If the coil never has given a spark, or a spark of at least 1/4-in. length, there is undoubtedly a break in the primary or secondary winding, probably the latter. Test windings by sending the current from two or three cells of battery through them, and by means of a galvanometer learn if a current flows through windings. If not there is a break and rewinding will be necessary. You also omit to mention vibrator. Has coil been fitted with one ? If so, make it vibrate with a small stick, and watch for results from secondary. A simple galvanometer can be made from a cheap compass-placed over a few turns of wire on a block of wood.

India furnishes 56 per cent of the world's output of mica, while the United States and Canada produce nearly all of the remainder.

The highest concrete chimney ever built is located at Tacoma, Washington. It is 307 feet high and was designed for a smelter to carry away the deadly fumes developed in the reduction of the ores so that the surrounding vegetation will not be injured or the residents in the vicinity annoyed.

In May, during the progress of some excavations on the estate of Lord Normanteau, near Crowland, Peterborough, Eng., workmen exposed a subterranean forest some ten feet below the surface and about three acres in extent. Some of the trees were in an admira-able state of preservation, and one large oak measured fifty-four feet in length. Although buried for unknown ages, the trees were found in such state of preservation that different kinds of wood could easily be determined. A kind of fir tree was most abundant. The surrounding clay contains quantities of remains of lower animal life.