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Lamps and


Three-Way Switch

Fig. 2.

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Answer: Referring to sketch No. I, the full lines represent the part which you show. The sketch has been completed with dotted lines indicating the proper method of wiring to obtain the desired result. One turn of the switch will throw off the light which is burning, and throw on the other, in every case. The wiring shown in sketch No. 2 is entirely correct for the three-way switch as it is used for the purpose of controlling a light from two separate points. The light can be turned on or off from either of the two three-way switches shown.


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The Wesco Supply Co.

St. Louis, U. S. A.

Probable M. E. P. of Steam Engines

Question: Please explain how to find the Mean Effective Pressure of a 6 x 12 steam engine making 250 revolutions per minute, the boiler pressure being 80 pounds by gauge.F. J.

Mention The Technical World.



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O, Off on Catalogue Prices

CONSULTING DEPARTMENT-(Continued) Answer: Your question cannot be given an absolute answer, for the reason

tors than those which you have given.


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OUR SPECIALTY: Strings for the professional trade.

know the cut-off, the back pressure, and type of engine. Making certain assumptions, we can give you an approximate answer. If the cut-off is 14, then the ratio of expansion is 4, neglecting clearance. Assuming the back pressure to be 3 pounds gauge, then the M. E. P. can be found by the formula

M. E. P.=p1+hyp. log. R
in which

P= Absolute initial pressure.
R=Ratio of expansion.

p= Back pressure (absolute).
Since the gauge pressure is 80 pounds, P
is 80 + 14.7 (= 94.7) pounds; R we
have assumed to be 4; and p is 3 + 14-7
(= 177). Substituting in the formula,
we have:


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- 17.7


= 56.5—17.7 = 38.8 pounds. We have made no allowances for losses due to compression, clearance, condensa

tion, wire drawing, etc. To allow for is a power plant paper for engineers-for those who install, operate and care for machinery, whether steam, these in a plain slide-valve engine, it is electric, gas or hydraulic.

customary to multiply this theoretical The issues of one year contain about one thousand

M. E. P. by the factor .8, which will pages of reading matter. The articles are in the highest degree educational, and of the most authoritative give us for the probable M. E. P., 38.8 x character. Every phase of every power plant subject is treated in a manner both popular and interesting.

.8 (= 31.04) pounds. ISSUED TWICE A MONTH. ONE DOLLAR A YEAR In the formula used above, you will Write for free sample copy.

find the term “hyp. log. R.” We are to The ENGINEER PUBLISHING COMPANY substitute for this term the hyperbolic 357 Dearborn Street,

CHICAGO, ILL. logarithm, or, as it is sometimes called,

the Napierian logarithm of the factor R. These logarithms will be found in almost

any engineer's handbook. The wonderful new power: maximum efficiency: minimum bulk. Especially adapted for marine or anto use. The best stationary power for electric lighting or other high speed purposes. Catalogue on request if you mention THE TECHNICAL WORLD,

Exhausting Under Water Cushman Motor Co., Lincoln, Neb. Question: Is it possible for two-cycle gas

engines to exhaust under water without seri-
ously reducing the H. P. of the engines?-
B. O.

Answer: This is frequently done

without loss of H. P. by extending the SECURED OR FEE RETURNED FREE opinion as to patentability. Send for Guide

terminal under water, with a small vent Book and What To Invent, finest publication is above the water. The vent prevents the sued for free distribution. Patents secured by us advertised free. EVANS, WILKENS & co.

water from drawing back to the muffler No. 600 F Stroot, N. W. Washington, D. C. when the motor stops.

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The Cushman Motor



( Model “H.” Capacity four passengers. Speed up to twentyfive miles an hour. $850. Equipped with tools, oilers, pump, repair kit, brass oil side lamps and brass horn.

( In this model the speed is regulated by the trottle attached to
the steering wheel, requiring only one hand to steer and control.
The ignition is timed automatically by a governor in exact require-
ment to the speed of the engine. Brakes both on transmission and
rear wheels. Power sufficient for grades up to forty per cent.

( Made in our own factory where the facilities are so complete that they involve the making of bolts and nuts even. These exactly fit the spanner wrenches which go with our vehicles.

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Preparation for College

CONSULTING DEPARTMENT-(Continued) Current of Open and Closed Motor

Question: Upon the name plate of a G. E. 500-volt direct-current compound-wound motor is the following:

"Open....10 H. P.....17 amperes.

Closed....572 H. P.....10 amperes."
Will you kindly explain the meaning of this? -
H. C. J.

Answer: This doubtless refers to the condition of the machine running in the

first place as an open motor, and in the JF Main Building, Armour Institute of Technology

second as an enclosed motor. It will be noticed that a current of 17 amperes is allowed in the first case, or when the machine is running as an open motor; and a current of only 10 amperes, when the machine is running as a closed motor. This discrepancy is, of course, due to the

difference in ventilation, the open motor BY MAIL

being much better ventilated than the Instruction under the direction of the regular

enclosed. teachers in a resident engineering college.

Lessons prepared especially for home study by teachers of acknowledged standing.

Domestic Heating System The full College Preparatory Course covers the entrance requirements of such a college as ARMOUR

Question: I wish to put a heating system INSTITUTE OF TECHNOLOGY, and students

in my house. Kindly give me some rules by satisfactorily completing this course are admitted

which I can determine the size of pipe necesto the college of engineering of that institution without further examination in the subjects taken.

sary, the dimensions of radiators, etc.-H. B. An unusual opportunity for young men of limit

Answer: Your inquiry is entirely too ed means to prepare for entrance to an engineering college without leaving home or interfering indefinite, since there are so many variwith their regular work.

able factors connected with any heating PARENTS wishing to KEEP THEIR

system, and you have omitted to state the CHILDREN AT HOME as long as possible before sending them to college will

exact conditions. The principal points find these courses of great value. There

to be considered are:- First, the system is no breaking of home ties, and the student not only has many of the ad

itself, i. e., whether a furnace, steam, or vantages of a private tutor but also the

hot water is to be used. Second, the sympathy and encouragement of his parents.

location and exposure. Third, the maThis is an excellent opportunity for teachers and terial of which the building is constructothers to take up engineering studies in their own

ed, and the purpose for which it is to be homes and at their own convenience under the guidance of resident school teachers.

used. The following general rules can In addition to the College Preparatory Course be used for rough calculation; but when instruction is also offered in

it comes to actually laying out the plant, Mathematics (Arithmetic, Algebra, Geom

more exact rules which necessitate the etry and Trigonometry), Electrical, Mechanical, Steam, Sanitary and Civil

knowledge of the conditions outlined Engineering: Architecture, Mechanical

above, should be used.
Drawing, Telegraphy, Telephony and
the manufacture of Textiles (Spinning,

Using steam, one square foot of direct
Weaving and Knitting).

radiation will supply from 60 to 80 cubic 200 page illustrated Bulletin, giving full infor

feet in ordinary dwellings. If indirect mation as to courses, teachers, methods of study. etc., may be had upon request.

radiation is used, these figures would be

from 40 to 50 cubic feet. If hot water of American School of Correspondence

high temperature is used, one square foot at

of radiation will take care of 50 to 70 Armour Institute of Technology

cubic feet; and if low-temperature hot CHICAGO, ILL., U.S.A.

water is used, these figures should be - Mention The Technical World, Dec. i

from 30 to 50. Mention The Technical World.

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