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California

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VIA

Union Pacific

FASTEST TIME

SHORTEST LINE
SMOOTHEST TRACK

Millions have been spent in the improvement of this line, and all human ingenuity has been adopted to protect its patrons against accident. The line is renowned for its fast trains and the general superiority of its service and equipment.

Tourist Sleepers a Specialty

Inquire of

E. L. LOMAX, G. P. & T. A. Omaha, Neb.

Current for Duplex Telegraphy-Telephone Receiver Magnets

Question 1: Is it not a fact that the system of duplex telegraphy, where an "artificial" resistance is used to force an equal division of current, requires about twice as much battery as an ordinary two-instrument line?

Question 2: What is the object or function of the permanent magnet of a telephone receiver?-B. E. J.

Answer 1: It is a fact that in the duplex system of telegraphy commonly used, twice as much battery is required as in a two-instrument single line of the same length. The reason for this is that the current in the artificial line, flowing as it does around the coils in a direction opposite to that in the main line, cuts down the magnetic pull of the main-line current to one-half. As an example, on the duplexes between New York and Buffalo, they use 200 volts at each end on wires having about 5,000 ohms' resistance. When opposite poles are to the line, this would give a current of 80 ma. on an ordinary line; but in the polar duplex this current is opposed in each polar relay by a current of 40 ma. in the opposite direction, so that the resultant in the relay is only 40 ma. A duplex has recently been invented in which this defect is eliminated.

Answer 2: The permanent magnet in the telephone receiver serves to hold the diaphragm in a state of strain, so that it is thus more fully under the control of the field; also the field is intensified. The practical effect of doing away with the permanent magnet would be to reduce the distinctness of articulation. using a permanent magnet, it exerts an attraction of its own on the diaphragm, which is increased or decreased by the current according to its direction.

Mention The Technical World.

In

Complete
Drawing
Outfit No. 3

The Official Drawing
Outfit Used and Re-
commended by the
School

REGULAR
RETAIL
PRICE
$15.84

(Cut is Reproduced
from a Photograph)

DETAILED LIST OF OUTFIT ILLUSTRATED:

INSTRUMENTS:

Set of German Silver Drawing Instruments in Morocco Leather Pocket Case, velvet lined, with bar and lock, comprising:

One German Silver compass, 6 inches long. with pen, pencil, needle point and lengthening bar.

One German Silver spacing dividers, 5 inches long.

One steel spring bow dividers, 34 inches long. One steel spring bow pen, 3 inches long, with needle point.

One steel spring bow pencil, 3% inches long, with
needle point.

One 5-inch ruling pen, spring on upper Blade.
One case with leads.

One adjusting key,

Retail Price of Instruments, $6.90

Total Value of Complete Outfit, $15.84

DRAWING MATERIALS:

One Drawing Board, 19x25 inches, seasoned pine,
with hardwood ledges, attached to board by
screws sunk in slots with metal bushings to
allow for contraction or expansion. Shellac
finish,

One Mahogany T-Square, 24 in. long, ebony
lined, fixed head, shellac finish,
One 450 Transparent Triangle, 8 inch,
One 300x600 Transparent Triangle, 10 inch,
One 12-inch Triangular Boxwood Scale, engine
divided; graduated 3-32, 3-16, 1-8, 1-4, 3-8, 3-4,
1-2, 1%, and 3 inches to the foot, and one edge
inches and 16ths, with case,

$2.00

.90
.75

.70

1.00

One Transparent Combination, Irregular or
French Curve, special.

1.00

One Bottle Waterproof Ink

.25

One 4-H Siberian Drawing Pencil,

.10

One Faber's Ink Eraser, No. 1075,

.05

One Faber's Pencil Eraser, No. 111,

.05

One dozen Thumbtacks,

.20

Nine sheets Whatman's handmade, cold pressed,
Drawing Paper, 13x20 inches,

.54

.15

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Twelve sheets Whitstock Drawing Paper, 11x15
inches (for practice work only),

SPECIAL PRICE TO A. S. C. STUDENTS an United States $6.95

and Canada Only)

In order to secure the above special price it is necessary to be a student of the American School of Correspondence. Orders should be sent direct to the address of the manufacturer as given below, accompanied by Post Office Order or by Registered Letter for the amount and a statement that the writer is a member of the American School of Correspondence. Express charges are to be paid by the purchaser (for students in the West and Middle West express charges to CHICAGO will be prepaid.) Address:

A. D. MACLACHLAN, 214 Clarendon Street, Boston

ARCHITECTS' AND ENGINEERS' SUPPLIES

507

Builders'

Architectural Drawing Self-Taught

TH

By FRED T. HODGSON

HIS work is especially designed for those who desire to learn drawing at home, a description of drawing instruments and accessories, with rules for using them, and hints as to their care and management. Rules for laying out simple drawings and executing same. The student is taught step by step to draw to scale, first the plans, next the elevations, and finally the details of a cottage, including foundations, walls, doors, windows, stairs, and all other items required for finishing a small building complete in every particular.

A chapter and a number of plates are devoted to more elaborate work, and the student is shown by a series of easy lessons in simple language how to make more elaborate drawings. Theory is not considered in the work, nor is perspective or shading, as the author has endeavored to make the work a purely practical one for practical workmen. Nearly all the examples given are drawn to scale and may be followed as they are given or may be enlarged or reduced at the will of the student. As an Architectural Drawing Book for real practical workingmen, who intend making draftsmen of themselves by their own efforts, this book has no equal.

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CONSULTING DEPARTMENT-(Concluded)

Step-Up Transformation

Question: I have a small step-down transformer-110 volts to 10 volts-with removable 10-volt secondary. Is it possible to build a secondary to raise the voltage from 110 volts to 220 volts and 3 amperes, using the same primary? My present primary is wound with No. 20 wire of 7 ohms' resistance.-H. H. P.

Answer: In order to obtain 3 amperes at 220 volts from the secondary, it will be necessary to supply the primary with 6 amperes and 110 volts. Your primary winding of No. 20 wire would not carry this current safely, and accordingly it cannot be used. If the size of your primary winding were sufficient to carry 6 amperes safely, then there would be no reason why you could not make the changes you suggest. You would simply need to put twice as many turns on your secondary as you have on your primary, and use a size of wire which will safely carry 3 amperes.

Milling Machine Dividing Head Question: How can I cut a triangle on a milling machine so that two of the angles shall be each 671⁄2°, and the other 45°? In other words, how many turns must I give the index pin, if it requires 40 revolutions to one revolution of the spindle?-G. M. M.

Answer: Since 45° is 8th of 360°, the work must be given th of a turn to obtain the angle required. Since 40 turns of the index pin are required for one revolution, it would require th of 40 (or 5) turns to make the angle of 45°. For the angle of 672°, we first find the fraction of a total revolution. This is: 67.5 3

360 16

Now, 3/16 of 40 revolutions equals 71⁄2 revolutions. Therefore we must give the index pin 7 complete turns, and then 1⁄2 a turn. The half turn can easily be made by moving the pin over 1⁄2 the number of holes on a circle of the index-plate containing an even number.

I have a 10 volume set of Engineering books which

I will dispose of at a bargain. Address,

M. B. RICHARDS,

3528 Lake Ave., Chicago, Ill.

"I'LL have you know that I belong to London!" said the tourist.

''Deed, an' wha'd hae thocht it?" quoth the skeptic Scot. "Frae the way ye've been speaking I thocht London belonged tae you."

Mention The Technical World.

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Foot and

"Star"Lathes Power

High grade screw cutting engine Lathes, with forged crucible
stee hollow spindles, phosphor bronze bearings, gear-driven
reversible feeds with strong friction drive in apron, patented
spring nuts which allow quick shift of change gears, also
Draw-in Chuck, Gear-cutting, Milling and Taper Attachments
if desired.

Suitable for electrical and repair work, model makers,
gunsmiths, technical schools and fine, accurate ma-
chine shop and tool room service. Ask for Catalog B.
(78)

The Seneca Falls Mfg. Co.

115 Water Street Seneca Falls, N. Y., U. S. A.

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ELECTRICAL BOOKS

We can furnish you with any work desired, including all of the LATEST
AND BEST, and covering the entire technical field

All Books sent, Postage Prepaid, upon receipt of Lowest Pub-
lisher's Price. Write for our New Catalogue.

Publishers, "SOUND WAVES" 1362 Monadnock Building

CHICAGO, ILL.

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