CONSULTING DEPARTMENT-(Continued) Star vs. Delta Connection Question: Please explain the advantage of the Star connection over the Delta connection in the three-phase generator for long-distance transmission.-A. Answer: In the case of the Star connection, the voltage between the mains is V3 times as great as that over the coils, while the current in each main is the same as that in the corresponding coil. In the case of the Delta connection, the voltage between the mains is the same as that over the coils, while the current is V3 times as great in the mains as in the coils. On this account, the Star connection is more suitable for long-distance transmission than the Delta. Horse-Power of Triple-Expansion Question: Please let me know through THE TECHNICAL WORLD, the formula for figuring the H. P. of a triple-expansion engine by condensing the M. E. P. of the cylinders to the low pressure; sizes of cylinders, 28 inches, 48 inches, and 72 inches; stroke, 42 inches; vacuum, 26 inches: piston travel, 200 feet per minute; boiler pressure by gauge, 160 pounds. -W. J. O. Answer: In reducing all the pressures to the area of the low-pressure cylinder, the same general formula as for a simple. engine can be used; that is: in which P is the sum of the total M. E. P.'s referred to the low-pressure cylinder; L, the length of stroke in feet; A, the area of the low-pressure cylinder in square inches; and N, the number of strokes per minute. To reduce the M. E. P. of each cylinder to the corresponding pressure on the low cylinder, you Electric Novelties and Supplies must multiply the M. E. P. of the cyl inder under consideration by the ratio of its volume to the volume of the lowpressure cylinder. If, as is usually the case, the stroke is the same in all cylinders, then the ratio of the volumes will be the same as the ratio of the squares of the diameters. For instance, the ratio of the intermediate to the lowpressure cylinder is: Fan Motor and Battery ....2 to $10.00 Telephone, complete.... .2.50, 3.00 10.00 5.95 Electric Door Bells.... Electric Carriage Lamps. 5.00 Electric Lanterns.. .2.00, 3.00 $8.00 Medical Batteries.. $12.00 Belt, with Suspensory Telegraph Outfits.. 2.00 Battery Motors.. 75c to 12.00 Bicycle Electric Lights. Electric Railway. 3.50 3.25 Necktie Lights.. Agents Wanted. Send for Free Book. Mention The Technical World. Pocket Flash Lights.......1.00 to 2.50 1.00 OHIO ELECTRIC WORKS, Cleveland, O. STUDY ENGINEERING BY MAIL.-The demand for has never been so great Send for particu- AMERICAN SCHOOL OF CORRESPONDENCE D CONSULTING DEPARTMENT-(Concluded) Multiplying the M. E. P. of the intermediate cylinder by 4/9, we would have the pressure referred to the low cylinder. Similarly, the pressure on the high can be determined; and if we add the M. E. P. of the high and intermediate (referred to the low) to the M. E. P. of the low itself, we have the total M. E. P., or the value of P in the formula. Of course the M. E. P. mentioned above cannot be determined accurately without the aid of the indicator diagram. If the piston speed in feet per minute is given, then the terms L and N in the formula can be omitted, and the piston speed substituted. Cement for Leather Question: Give formula for quick-setting cement for leather belts, that oil will not affect.-A. W. N. Answer: Take 16 parts gutta-percha, 4 India rubber, 2 pitch, 1 shellac, 2 linseed oil. Cut small, melt together, and mix well. Resistance of Ground Question: Please give me formula for the resistance of a ground by the voltmeter method.-F. W. W. Answer: This can be found by using a Weston voltmeter as follows: Connect one side of the circuit to one bindingpost of the voltmeter, and connect a water pipe to the other binding-post of the voltmeter. If now there is any deflection, we know that there is a ground on the opposite side of the circuit from that to which the voltmeter is connected. The resistance of this ground may be found by the formula: Mention The Technical World. MANHATTAN ELECTRICAL SUPPLY CO., 187 5th Ave., Chicago NEW YORK-32 Cortlandt St. 39 Dey St. JERSEY CITY-42-46 Essex St. 41-47 Morris St. Stately Homes in America By HARRY W. DESMOND and HERBERT D. CROLY Size 81⁄2 x 101⁄2 inches. 532 pp., gilt top, cloth binding, fully illustrated. Price, $7.50. T HIS work illustrates the development of fine residences built in this country from the Colonial period to date. Many fine homes are pictured for the first time the great Vanderbilt Mansions and others of that class. The text is a serious attempt to explain social and economic conditions and architectural developments which have produced these sumptuous buildings. Architectural Record, 14-16 Vesey St., New York PERSONAL AND MISCELLANEOUS THE A Well-Deserved Honor HE CHAIR of English Literature in Armour Institute of Technology, rendered vacant by the call of Prof. F. M. Tisdel to the presidency of the Uni versity of Wyoming, has been filled by ledge, Dean of the American School of the appointment of Dr. William A. Col Correspondence. This means, of course, a loss to THE TECHNICAL WORLD, for with this number Doctor Colledge severs his active connection with the editorial board of the magazine. We congratulate Doctor Colledge on the enlarged opportunities opened up to him in his new field as a member of the Faculty of Armour Institute of Technology, and the Institute on securing his services. The Editors hope still to be favored with his able advice on matters connected with the magazine. THIS Electricity in India HIS GREAT ENERGY, which is the leading feature of the day in nearly all parts of the world, but chiefly in America, has of late years been making gradual progress in the greatest of British possessions in the East. Commencing from the south, it may be interesting to note how the Government of Mysore has endeavored to improve her state by the use of electricity derived from power from the natural waterfalls of the Cauvery. Gold mining by this great unknown power has already proved a success, and various large extensions and improvements under leading British and American firms are in progress. The Presidencies of Madras and Bombay, though somewhat late in the field, have at present schemes for the improvement of their capitals; and even the great Mention The Technical World. |