March 29, 1889.] 



SCIENCE. 



235 



with turned-up edges, and an extinguisher of tin plate should be at 

 hand to place over the whole apparatus. No Leyden jars should 

 be included in the electrical circuit. The difficulties which for- 

 merly arose in the exhibition of experiments in statical electricity, 

 owing to the presence of moisture in the air of a lecture-room, are 

 now immensely reduced by the Wimshurst machine, which worlds 

 with unfailing certainty under adverse conditions. A new and 

 very beautiful machine was Ivindly lent by Mr. Wimshurst for the 

 purposes of the lecture. 



Arc-Lamp For Incandescent Circuits. — The Silvey 

 Electric Company, Lima, O., claims to have the only arc-lamp that 

 can be depended on at all times for incandescent circuits. In this 

 lamp it is impossible to cross the carbons or cause a short-circuit. 

 The lamp has a rack feed-rod fed by a mechanism which makes it 

 impossible for the carbons to approach each other more than one 

 two-hundredth part of an inch at a time, thus maintaining the light 

 steady at all times, while it is impossible for the two carbons to 

 drop together. The light may be turned on or off at will, and the 

 ■company guarantee the lamp to burn perfect upon any system of 

 incandescent lighting, and to not interfere with the incandescent 

 lights. Persons having incandescent machines often want an arc- 

 lamp or two for yards or large open places. This lamp meets this 

 want, and is arranged to burn on the Edison, Mather, Thomson- 

 Houston, United States, and other incandescent machines. It 

 takes the same amount of power as ten incandescent lamps, giving 

 a return of two thousand nominal candle-power. A patent was 

 issued to William L. Silvey, March 5. 



Dynamo-Designing. — At a meeting of the Engineers' Club 

 of St. Louis, March 20, Professor Nipher addressed the club on 

 " Plans of Investigations in Dynamo-Designing." His remarks 

 were illustrated by numerous drawings, and by formulse and 

 sketches on the blackboard. He explained in detail the principles 

 involved, and showed how, when certain constants for any type of 

 dynamo had been ascertained, the design of dynamo of the same 

 type of any other desired capacity could be readily determined. He 

 had recently made such a calculation for an Edison dynamo, which 

 he used as an illustration. He gave two empirical formula for 

 the safe carrying capacity of a wire in amperes. The cost of cop- 

 per necessary in any dynamo, and the speed at which it could be 

 run, were usually determining factors in the problem. Another 

 important consideration is the resistance which the space around 

 the dynamo offers to the magnetic line. It would be very desirable 

 to have experiments made to determine this resistance for the 

 prominent dynamos now in the market. 



The Magnetic Action of Displacement Currents in a 

 Dielectric. — Professor S. P. Thompson read before the Royal 

 Society a few weeks ago an interesting paper on displacement cur- 

 rents. That there is an electric displacement in the dielectric of a 

 condenser when the coatings are charged, and that any variation 

 of this displacement causes effects analogous to those of ordinary 

 electric currents, are points that have been indirectly proved by sev- 

 eral experiments, notably those of Hertz. Thompson attempted at 

 first to prove it directly by observing the effect on an astatic needle 

 suspended near the edge of a condenser, of charging the condenser 

 or of discharging it. But, as calculation showed that the effect 

 would be too small to be observed, he adopted a different method. 

 An iron annulus wound with a coil of fine wire was embedded in a 

 layer of paraffine between two glass plates which were coated with 

 tinfoil. The displacement passes through the iron ring, and any 

 changes in the displacement should set up lines of magnetic induc- 

 tion in it ; and these would cause currents in the fine wire circuit 

 with which it was wound. The condenser was connected with an 

 induction-coil ; the fine wire, with a telephone. When the induc- 

 tion-coil was working, sounds were heard in the telephone, and it 

 is held that this proves the existence of displacement currents. 

 The method is extremely simple and ingenious ; but one is led to 

 ask if the reasoning that deduces from the experiment the existence 

 of displacement currents does not depend on assumptions no better 

 proved than the phenomenon experimented on. 



Patents on Alternating-Current Transformers. — 

 Some months ago the validity of the Gaulard and Gibbs patents in 



England suffered an adverse decision of the courts, and the decision 

 has just been affirmed by the Court of Appeal. In this country 

 theGaulard-Gibbs patents are held by the Westinghouse Company ; 

 and, although decisions of English courts do not by any means 

 allow us to infer how the same case would be decided here, yet the 

 result could not but be a blow to that company. As an indirect 

 result of the trial, however, the Jablochkoff patents have been 

 brought prominently forward ; and as it is understood that the 

 Jablochkoff patents in this country are owned by the United States 

 Electric Lighting Company, and as the United States Company is 

 controlled by the Westinghouse, the position of the latter corpora- 

 tion is not materially weakened by the English decision. M. Ja- 

 blochkoff had granted him in 1877 a patent, of which one claim 

 read as follows : " The use in apparatus for the production of elec- 

 tric light, of induction-coils, interposed in a primary electric circuit 

 for generating separate and independent currents, to be used for 

 producing electric light in one or more lamps interposed in such 

 secondary circuits substantially as herein described." It is under- 

 stood that the owners of the English patents have made arrange- 

 ments with some of the leading electrical manufacturing concerns 

 in that country by which the latter have been granted licenses under 

 the patents. 



The Tesla Alternating-Current Electric Motor. — 

 Almost a year ago Mr. Tesla read before the Institute of Electrical 

 Engineers a paper on alternating-current electric motors, in which 

 he described a motor of his own invention, which embodied several 

 novel and ingenious features. The great novelty of the invention 

 consists in the fact that the revolving armature is not connected 

 with any external source of supply, but has currents induced in its 

 coils by the variations of the magnetic field. The motor attracted 

 a great deal of attention at the time, and its performance was en- 

 thusiastically praised. Professor W. A. Anthony made tests of the 

 motor, but the only datum he gave was, that, " at 6,400 alterna- 

 tions, over one horse-power can be obtained at an efficiency of 62 

 per cent." As the measurement of the efficiency of such a machine 

 would be extremely difficult, embodying some novel methods, and as 

 no details of the methods employed or of the weight or speed of 

 the motor were given, we can hardly consider Professor Anthony's 

 statements as very satisfactory, and now we are again disappointed. 

 A Tesla motor was sent to the Central Institution in London, 

 and we had hoped that some tests would be made and pub- 

 lished ; but the only information so far obtained is a statement of 

 Professor Ayrton that the motor gave .63 horse-power with 3,720 

 alternations at a speed of 3,200 revolutions, — quite an impractical 

 speed for a commercial machine. The Tesla motor has been taken 

 up by the Westinghouse Company, and there is no doubt that neither 

 energy, nor money, nor talent are being spared to develop it. There 

 is no doubt that it will work, artd there is little doubt that it offers 

 some advantages. At present it labors under the disadvantages of 

 not being applicable with an ordinary alternating-current system, 

 of requiring three wires instead of two, and of being possibly not 

 so light or as efficient as a corresponding continuous-current motor. 

 In a short article on the subject, the London Electrical Review 

 concludes : " The weight of material used in a Tesla motor must 

 be several times as much as that necessary for a continuous-current 

 motor to give the same output, rendering such machines very 

 costly. Thus it would appear that alternating-current motors are 

 a long way off from the ideal goal, in spite of the strenuous efforts 

 on the part of some of the smartest people in the world ; and we 

 are inclined to think that the solution of the problem may yet have 

 to be sought in an entirely different direction." This is rather 

 gloomy, and is hardly consistent with the fact that the subject has 

 made rapid strides in the last year, and gives promise of an early 

 solution of the whole question. 



The Birmingham Electric Locomotive. —This locomotive 

 is used for exceptionally heavy tramway work, and was designed 

 to take the place of the steam-engines now in use. The motor 

 weighs a ton, and the current for it is supplied from 100 storage- 

 cells, weighing together four tons and a half. The cells are sub- 

 divided into four groups, which can be used either four in parallel, 

 two in series, two in parallel, three in series, or four in series. The 

 motor is suspended beneath the car, and is geared directly to both 



