Our readers are invited to contribute to this department, but no responsibility is assumed for the opinions expressed in these communications.

Letters for this department should be addressed to Editor of Amateur Work, 86 Water Street, Boston.

They should be plainly written on only one side of the paper, with a top margin of one inch and side margins of one-half inch.

The name and address of the writer must be given, but will not be used, if so requested.

Enclose stamps, if an answer is desired.

In referring to other letters, give the number of the letter referred to, and the date published.

Illustrate the subject when possible by a drawing or photograph with dimensions.

Readers who desire to purchase articles not advertised in our columns will be furnished the addresses of dealers or manufacturers, if stamp is enclosed with request.

(No. 13.) Providence, R. I., April 1, 1902.

Can you tell me where I can get the numbers like those used on the "old Dutch clock" described in the December number of Amateur Work?

J. J. B

The hardware dealers of your city should be able to supply you with these figures; they are the kind used for numbering doors, and come in several sizes. The dealer should be able to send and get them if he does not carry them in stock. It would not be a difficult matter to make drawings and saw them out of sheet brass, as described in the April number.

(No. 14.) Malden, Mass., April 10, 1902.

Please advise what kind of stain to use on the Dutch furniture described in the magazine, to get the dark effects seen on similar furniture sold by furniture dealers. C. E. P.

The dark effects are probably secured by using aniline colors, which may be obtained from any large dealer in paints. The dark green is a mixture of black and yellow; the dark brown, by adding a little black to the brown ordinarily sold. An ounce package of aniline costs from 15 to 25 cents, according to color, and will be sufficient for several pieces of furniture. It is mixed with alcohol and put on with a brush and, when dry, the surplus color is rubbed off with a piece of cloth. A coating of wood stain is sometimes added after the aniline color, but this is a matter of personal choice. A little experimenting with waste pieces of wood will enable the correct color to be ascertained. A final coating of thin shellac is given to prevent wearing.

(No. 15.) Providence, R. I., April 11, 1902.

1. Will you kindly explain what is the principle on which Nicola Tesla's " condensing oscillator " works? He claims that it does away with the induction coil. He says : " My oscillator involves the use of vibrations of an electrical condenser which stores electrical energy. This energy is of an explosive nature. When this energy is suddenly released, as in my machine, it produces quickly vibrating oscillations. Though this energy may be enormous in amount, it is not harmful in nature. By means of this machine I may pass half a million volts of electricity through a man without injury." Will you explain what he means by quickly varying oscillations? Does electricity oscillate or travel spirally in this case?

2. Can you tell me if Marconi has a ground or water connection in his wireless telegraphy apparatus ?

O. L. L

1. An "oscillator" consists of a secondary coil in which a current of electricity is induced by a primary coil, through which a current of electricity from a condenser (Leyden jar) is passing. There is no iron core required, and the primary and secondary coils have few turns of wire. When electricity accumulated in a condenser, for instance a Leyden jar, is caused to pass through an insulator, i. e., when a disruptive discharge takes place, the cuirrent does not simply flow, but appears to oscillate to and from very rapidly, according to the size of the condenser. The high frequency current spoken of appears to travel on the surface of the conductors, and therefore is harmless when passing over the body.

2. Marconi in his wireless telegraphy apparatus has one side of his coherer connected with the earth, also one side of his transmitter.

(No. 16.) Providence, R. I., April 17, 1902.

I am making a dynamo of 11/4 H. P., but have not been able to get the discs for the armature] core at a reasonable price. Can you tell me where I would be likely to get them? I want discs 6' in diameter, 1/32 thick, with 11/2" hole in center. H. M., Jr.

Carlisle & Finch Co., Cincinnati, Ohio, sell discs for armatures, but I am not advised whether they have the size you desire or not. In the event of their not having them, they can be cheaply made as follows: Procure sufficient soft sheet iron, have same cut on a shearing machine into pieces a trifle over 6" square. Drill 11/2" holes in the center of each piece. When drilled put them on a 11/2" bolt long enough to contain them all, and fasten firmly together by screwing the nut tight. On the top piece scribe a circle 6" in diameter, and along this circle, but partly inside of it, drill holes for the wiring. These holes are of the size and number which the wiring requires, according to design. The discs are then mounted on an arbor, put in a lathe and turned down. In this way, armature discs can easily be made of any size.