289. Copper. Sheet-copper can be purchased at a tinsmith's or at a hardware store. Electricians usually have a thin variety of copper called brush copper, which makes good battery-plates, binding-posts, etc. You can cut this thin copper with an ordinary pair of shears.

290. Iron. For thin sheet-iron, nothing is better than sheet-tin. (See tin.) Hoop iron is thicker than tin, and makes good yokes, etc. In many cases, ordinary nails may be used where a magnetic substance is needed.

Annealed iron wire is extremely soft. (See text-book for experiments with steel and iron.)

291. Steel. Old files, watch-springs, clock-springs, corset-steels, knitting-needles, harness-needles, hack-saw blades, sewing-needles, etc., are generally made of a good quality of steel.

292. Zinc, in the sheet form, can be bought at a hardware store. For a few cents you can get quite a large piece. Get the thick pieces for heavy battery-plates of an electrician. You do not need anything that is thicker than 1/8 in. The zinc rods are usually amalgamated.

293. Lead can be bought at a plumber's, tinsmith's, or hardware store.

You may want some for a storage cell.

294. Nails. Wire nails are best for light work. Get an a.s.sortment from 1/2 in. long up to 1-1/2 in.

295. Screws. It is better to use bra.s.s screws around electrical apparatus. For the small work, for binding-posts, etc., use 5/8 No. 5.

Another handy size is No. 7, from 3/4 to 1-1/4 in. long. The round-headed screws are best, unless you want to countersink them.

296. Tin. This is really thin sheet-iron, covered with tin. Save up tomato-cans, cracker-boxes, condensed-milk cans, etc. The cracker-boxes are just as good as sheet-tin, as the pieces are large and clean. You can remove the solder from cans by heating them in the kitchen fire.

Knock out the bottoms with a poker when the solder gets soft. Clean the tin with sand-paper.

297. Carbons. You can get carbon rods or plates at an electrician's. If you have arc electric lights in your city, you will be able to pick up carbons; these, however, generally have a coating of copper, which must be eaten off with dilute nitric acid. This is a bother. You will find it cheaper to buy the 1/2 in. rods that are 12 in. long, and uncoated.

298. Sh.e.l.lac. Your wood-work will be much improved by using sh.e.l.lac upon it after you have thoroughly sand-papered it. You can get it, all prepared, at a paint store. Wood-alcohol is used to thin it if it gets too thick. Keep it in a wide-mouth bottle. Paint it on quickly and evenly with a brush, and do not go over it again when it is partly dry.

Wait until it is thoroughly hard before putting on a second coat. It should be fairly thin to spread well. Clean your brush in wood-alcohol before putting it away, and keep the sh.e.l.lac bottle tightly corked. A small tin can or a teacup is best to hold the sh.e.l.lac when using it.

THINGS A BOY SHOULD KNOW ABOUT ELECTRICITY.

By THOMAS M. ST. JOHN, Met. E.

The book contains 180 pages, and 260 ill.u.s.trations; it measures 5 7-1/2 in., and is bound in cloth.

Seventh Edition Price, postpaid, $1.00

CONTENTS: Chapter I. About Frictional Electricity.--II. About Magnets and Magnetism.--III. How Electricity is Generated by the Voltaic Cell.--IV. Various Voltaic Cells.--V. About Push-b.u.t.tons, Switches and Binding-Posts.--VI. Units and Apparatus for Electrical Measurements.--VII. Chemical Effects of the Electric Current.--VIII. How Electroplating and Electrotyping are Done.--IX.

The Storage Battery and How it Works.--X. How Electricity is Generated by Heat.--XI. Magnetic Effects of the Electric Current.--XII. How Electricity is Generated by Induction.--XIII.

How the Induction Coil Works.--XIV. The Electric Telegraph, and How it Sends Messages.--XV. The Electric Bell and Some of its Uses.--XVI. The Telephone, and How it Transmits Speech.--XVII. How Electricity is Generated by Dynamos.--XVIII. How the Electric Current is Transformed.--XIX. How Electric Currents are Distributed for Use.--XX. How Heat is Produced by the Electric Current.--XXI.

How Light is Produced by the Incandescent Lamp.--XXII. How Light is Produced by the Arc Lamp.--XXIII. X-Rays, and How the Bones of the Human Body are Photographed.--XXIV. The Electric Motor and How it Does Work.--XXV. Electric Cars, Boats and Automobiles.--XXVI. A Word About Central Stations.--XXVII. Miscellaneous Uses of Electricity.

This book explains, in simple, straightforward language, many things about electricity; things in which the American boy is intensely interested; things he wants to know; things he should know.

It is free from technical language and rhetorical frills, but it tells how things work, and why they work.

It is brimful of ill.u.s.trations--the best that can be had--ill.u.s.trations that are taken directly from apparatus and machinery, and that show what they are intended to show.

This book does not contain experiments, or tell how to make apparatus; our other books do that. After explaining the simple principles of electricity, it shows how these principles are used and combined to make electricity do every-day work.

_Everyone Should Know About Electricity._

A VERY APPROPRIATE PRESENT

Things a Boy Should Know About Wireless

By THOMAS M. ST. JOHN, Met. E.

Author of "Things a Boy Should Know about Electricity," "Fun with Electricity," "The Study of Elementary Electricity and Magnetism by Experiment," "The Study of Electric Motors by Experiment," "Electrical Handicraft," Etc., Etc.

126 Pages--109 Ill.u.s.trations and Diagrams Bound in Cloth--Net $1.00

This book contains much practical and some theoretical information regarding the operation and explanation of wireless outfits. It discusses enough of the theoretical side to make the student sure of himself and to give a well-rounded knowledge of this most practical subject.

The author has explained the various pieces of apparatus needed in a wireless station in such a clear manner that the student can not fail to understand how they work and why they work. The numerous drawings and diagrams simplify the discussions to such an extent that the reader will not want to skip a single paragraph.

"Things a Boy Should Know About Wireless" will be welcomed by thousands of enthusiasts and it should find its way into every library.

From

THOMAS M. ST. JOHN

Cascade Ranch.

East Windham,--N.Y.

The Study of Elementary Electricity and Magnetism by Experiment

By THOMAS M. ST. JOHN, Met. E.

FOURTH EDITION Price, postpaid, $1.25.

The book contains 220 pages and 168 ill.u.s.trations. It measures 5 7-1/2 in., and it is bound in green cloth.

CONTENTS: Part I. Magnetism.--Chapter I. Iron and Steel.--II.

Magnets.--III. Induced Magnetism.--IV. The Magnetic Field.--V.

Terrestrial Magnetism. Part II. Static Electricity.--VI.

Electrification.--VII. Insulators and Conductors--VIII. Charging and Discharging Conductors.--IX. Induced Electrification.--X.

Condensation of Electrification.--XI. Electroscopes.--XII.

Miscellaneous Experiments.--XIII. Atmospheric Electricity. Part III. Current Electricity.--XIV. Construction and Use of Apparatus.--XV. Galvanic Cells and Batteries.--XVI. The Electric Circuit.--XVII. Electromotive Force.--XVIII. Electrical Resistance.--XIX. Measurement of Resistance.--XX. Current Strength.--XXI. Chemical Effects of the Electric Current.--XXII.

Electromagnetism.--XXIII. Electromagnets.--XXIV. Thermo electricity.--XXV. Induced Currents.--XXVI. The Production of Motion by Currents.--XXVII. Applications of Electricity.--XXVIII.

Wire Tables.--Apparatus List.--Index.