Light Switch Switch Three-Way Switch FIG. 2. Answer: Referring to sketch No. 1, 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. 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. PENBRTHY WHEN ALL AT SEA As to the best Boiler Feeder for your plant, pin your faith to The Penberthy It can be trusted to give always the same unvarying satis- The Penberthy differs from the usual "column" type, and is in every way Every engineer should have our catalog ready for instant reference. Write for it to-day, PENBERTHY INJECTOR COMPANY, 365 HOLDEN AVENUE, DETROIT, MICHIGAN, U. S. A. PENBERTHY INJECTOR COMPANY, LTD., WINDSOR, ONT. Penberthy Bulletin sent free for three months. $50% Off on Catalogue Prices Hereafter we will give to the public direct in full all teachers' and dealers' discounts on violins, guitars, mandolins, and other stringed instruments. Our standard Lewis Orchestra No. 1 violin (worth easily $25 to $30 among dealers; listed in our catalogue for years at $21; now $10.50 net direct to you). The famous Lewis Stradivarius model $65 violin for $32.50. Other values for from $3.50 to $125 and upward. We are the largest and oldest exclusive stringed instrument house in the U, S., and import direct from our own workshops in Eisleben, Germany, and Padua, Italy. Ten days' free trial of our instrument. Write for catalogue. WM. LEWIS & SON, is a power plant paper for engineers-for those who install, operate and care for machinery, whether steam, electric, gas or hydraulic. The issues of one year contain about one thousand pages of reading matter. The articles are in the highest degree educational, and of the most authoritative character. Every phase of every power plant subject is treated in a manner both popular and interesting. ISSUED TWICE A MONTH. ONE DOLLAR A YEAR Write for free sample copy. The ENGINEER PUBLISHING COMPANY 357 Dearborn Street, CHICAGO, ILL. CONSULTING DEPARTMENT-(Continued) Answer: Your question cannot be given an absolute answer, for the reason that the M. E. P. depends on other factors than those which you have given. In other words, it would be necessary to 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 We have made no allowances for losses due to compression, clearance, condensation, wire drawing, etc. To allow for these in a plain slide-valve engine, it is customary to multiply this theoretical M. E. P. by the factor .8, which will give us for the probable M. E. P., 38.8 × x .8 ( 31.04) pounds. In the formula used above, you will find the term "hyp. log. R." We are to substitute for this term the hyperbolic 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. Exhausting Under Water Question: Is it possible for two-cycle gas engines to exhaust under water without seriously reducing the H. P. of the engines?— B. O. Answer: This is frequently done without loss of H. P. by extending the terminal under water, with a small vent above the water. The vent prevents the water from drawing back to the muffler when the motor stops. Mention The Technical World. 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 requirement 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. The tonneau of Model "H" can be readily removed and the vehicle converted into a run-about, Model "G", and at slight expense delivery wagon top can be added. Send for THE RAMBLER MAGAZINE and other printed matter. Thomas B. Jeffery & Company MAIN OFFICE AND FACTORY, KENOSHA, WISCONSIN Main Building, Armour Institute of Technology Preparation for College BY MAIL Instruction under the direction of the regular teachers in a resident engineering college. Lessons prepared especially for home study by teachers of acknowledged standing. The full College Preparatory Course covers the entrance requirements of such a college as ARMOUR INSTITUTE OF TECHNOLOGY, and students satisfactorily completing this course are admitted to the college of engineering of that institution without further examination in the subjects taken. An unusual opportunity for young men of limited means to prepare for entrance to an engineering college without leaving home or interfering with their regular work. PARENTS wishing to KEEP THEIR This is an excellent opportunity for teachers and others to take up engineering studies in their own homes and at their own convenience under the guidance of resident school teachers. In addition to the College Preparatory Course instruction is also offered in Mathematics (Arithmetic, Algebra, Geom- 200 page illustrated Bulletin, giving full information as to courses, teachers, methods of study, etc., may be had upon request. American School of Correspondence at Armour Institute of Technology CHICAGO, ILL., U. S. A. Mention The Technical World, Dec. 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....5% 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 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 being much better ventilated than the enclosed. Domestic Heating System Question: I wish to put a heating system in my house. Kindly give me some rules by which 1 can determine the size of pipe necessary, the dimensions of radiators, etc.-H. B. Answer: Your inquiry is entirely too indefinite, since there are so many variable factors connected with any heating system, and you have omitted to state the exact conditions. The principal points to be considered are:-First, the system itself, i. e., whether a furnace, steam, or hot water is to be used. Second, the location and exposure. Third, the material of which the building is constructed, and the purpose for which it is to be used. The following general rules can be used for rough calculation; but when it comes to actually laying out the plant. more exact rules which necessitate the knowledge of the conditions outlined above, should be used. Using steam, one square foot of direct radiation will supply from 60 to 80 cubic feet in ordinary dwellings. If indirect radiation is used, these figures would be from 40 to 50 cubic feet. If hot water of high temperature is used, one square foot of radiation will take care of 50 to 70 cubic feet; and if low-temperature hot water is used, these figures should be from 30 to 50. Mention The Technical World. |