Ng. 127. So. Orange, N. J., Jan. 31, '06.

In an article recently published in Amateur Work on induction coils by Mr. Graves he says a coil should be wound in sections. Does he mean cross sections or length sections? Also, in winding, do you wind from the right side to the left and then from the left back again ?

Can you also tell me what size coil I will need for a wireless outfit to send messages about two miles ?

T. G. C, Jr.

By " sections " Mr. Graves means thin sections of pan-cake form, the number and thickness depending upon the size of the coil. These are wound to proper diameter between discs of cardboard which have been previously soaked in paraffine wax. The process will be fully described in an article now in preparation to-be published at an early date. The windings and connections between sections must be such as will send the current around the core and primary in the same direction. As it is more convenient, as well as less liable to short circuits, to connect the inside and outside terminals of adjacent sections together; every other section should be wound in the same direction, the inside terminal of one should be connected to the outside terminal of the next, the sections and separating discs being liberally coated with paraffine.

No. 128. San Francisco, CaL., Feb. 12, '06.

Will you kindly tell me how to avoid the spark at break between two sliding contacts without the use of a condenser?

I have two magnets each wound with 400 turns of No. 30 B. & S. gauge wire, connected in the usual form and use three dry cells for an electric clock making contact every minute, but the sparking oxidizes the contacts and makes trouble. The condenser, consisting of 100 4 x 6 sheets of foil, also limits the spark to a degree. T. W. H.

The spark at the breaking of the contact points is caused by the "extra current " or induced discharge of the magnet windings. Some form of condenser must be Used to prevent it. It may also be well to introduce about 30 ohms of fine insulated German silver magnet wire in series with the condenser. The added resistance will lessen the amperage of the condenser discharge and greatly reduce the tendency to spark. If this does not fully cure the trouble, we would suggest that you make a condenser of tin foil, separated by thin, strong paper and then roll in tubular form. Wrap fine twine about the package to hold it in shape, and immerse in paraffine wax.

Electrical traction on Swiss railroads is a new thing; but it seems only natural that Switzerland, so rich in "white coal," begins to utilize its wealth of water, and supersedes, by the power derived from it, the enormous quantity of coal imported from Germany, France, Belgium and England. This new trial of electrical power on such an important new line will be watched with keen interest. If successful, the new mode of traction will certainly be employed all over the country.