June 8, 1888.] 



SCIENCE. 



273 



ELECTRICAL SCIENCE. 

 Alternating-Current Electro-Motors. 



Two inventions that will greatly modify and improve the con- 

 ditions of electrical distribution have been for some years past the 

 subject of much thought and experiment among electricians. They 

 are the secondary battery and the alternating-current electro-motor. 

 To-day there are secondary batteries in use, and there are alter- 

 nating-current motors, that will run with some degree of success ; 

 but improvement is necessary in order that they may be adapted to 

 extensive operations, and it is only a matter of time when these 

 improvements will be made. 



The Tesla electric motor, of which a brief description has ap- 

 peared in this journal, seems the most successful attempt that has 

 been made for the distribution of power by alternating currents. 

 The difficulties in the way of such a motor are these: it must start 

 with the maximum turning effort; when it attains its proper speed, 

 at must regulate itself for varying loads ; and it inust be made to 

 work under constantly changing load ; and all these requirements 

 are difficult to fulfil in the same machine. In one form of motor 

 Mr. Tesla obtains synchronism between the revolutions of the 

 armature and the reversals of the feeding dynamo ; that is, it reg- 

 ulates itself. This form has little or no turning effort at the start. 

 In another type a considerable turning effort is obtained, but there 

 is no regulation. By combining the two characteristics, a motor is 

 produced that will start, and when it arrives at its proper speed 

 will regulate, itself. This seems the most plausible plan that has 

 been yet suggested for the purpose. It will be remembered that 

 the motor presents the peculiarity of having no connection between 

 the armature-coils and the external circuit, currents being induced 

 in the former by the alternations of the field-currents, and so is the 

 simplest mechanical and electrical arrangement possible. 



In a paper read before the Institute of Electrical Engineers, Mr. 

 Tesla explained the system, but unfortunately gave no data as to 

 the efificienc)', output, etc., of the motors. Such data will probably 

 be forthcoming, for such a promising invention cannot but be given 

 an exhaustive trial ; and it is to be hoped, that, when the data does 

 appear, it will be of a kind to at once allow an opinion to be formed 

 •on the value of \}l\^ principle as well as of the particular machine 

 tested. 



Electrical Welding. — Among the various uses to which 

 ■electricity has been applied, the welding of metals is one of the 

 latest. Two distinct processes are now in use, — that of Prof. 

 Elihu Thomson, and that of M. Bernados. In Thomson's method 

 a very heavy current is sent between the metals to be joined 

 (which are held firmly against one another), heating the junction 

 until it is to a welding heat. The junction is, of course, the point 

 ■of greatest resistance, and therefore the heat is mainly concentrated 

 there. The currents are obtained from the secondary of an induc- 

 tion-coil supplied with alternating currents : this secondary is of 

 very low resistance, and is secured to 'the pieces to be welded by 

 massive clamps. It will be seen that this method is especially ap- 

 plicable to the welding of tubes, rods, wires, etc. The process of M. 

 Bernados is very different. In it the heat of the electric arc is used, 

 the junction to be welded being made one of the poles. Current 

 is obtained from accumulators especially built to resist the ill 

 effects of a heavy discharge rate, and the arc is directed to the 

 proper place by a rod of carbon held in the hand in a suit- 

 able holder. The method of operation consists in placing the 

 pieces to be welded on a heavy iron slab, which serves the double 

 purpose of supporting and carrying the current to the plate, 

 meeting the edges of the pieces, then putting the scraps of iron (if 

 iron is to be welded) on the junction, and melting the whole to- 

 gether. For welding steel or wrought iron, a mixture of sand and 

 lime is used as a flux ; when copper is one of the metals used, 

 borax is employed. Mr. Ryves, who has investigated the process, 

 and has lately read a paper upon it before the Society of Telegraph 

 Engineers and Electricians, states that in nearly every case the 

 metal was badly burnt and spoiled by the excessive heat. M. Ber- 

 nados has also lately made a number of experiments on the work- 

 ing of various metals and the production of alloys in electrical fur- 

 naces. As far as welding goes, it is very probable that the electric 

 arc can be regulated to give the required heat without burning the 



metal. Of the two welding processes, that of Professor Thomson 

 is surer and more easily controlled ; that of M. Bernados is more 

 widely applicable. 



Difference of Potential between Metals in Solu- 

 tions OF Different Strengths. — The following table is not 

 without interest as showing the variation in the electro-motive force 

 of a cell, which might occur when the solution changed in strength 

 from evaporation or other causes. It is unfortunate that potassium 

 cyanide was chosen as the electrolyte, instead 7of some more com- 

 monly used substance. One curious result will be noticed: zinc 

 and copper have a potential difference from a carbon electrode 

 which is at first considerable ; but, as the strength of the solution 

 increases, the two substances get nearer together in the table. 

 Carbon was invariably used as the positive element. The differ- 

 ences of potential are in volts. 





/006 



.025 



.25 



■5 



- 



- 



5.16 







Zinc 







I 350 



i^395 



I.45U 



1.520 



1.615 





.250 

 .290 

 ■435 



.390 

 .58° 

 ■535 











'■535 













1.460 



Platinoid 



.825 



.goo 



•■545 



1.030 



1.18s 



German silver .... 



.360 



.500 



.860 



.920 



.910 



1.050 



1. 180 



Silver 



_ 





.655 



•695 



.760 



845 



.970 



Lead 



.460 



.440 



.590 



.5S5 



.610 



.640 



.700 





.230 



.300 



■539 



■ 450 



•430 



.470 



•455 







Expansion Galvanometer. — Prof. W. E. Geyer and Mr. W. 

 H. Bristor have invented a new and ingenious galvanometer. In 

 thermostats and in the balance-wheels of chronometers the differ- 

 ence in the rate of expansion of two metals is taken advantage of 

 to cause a movement, which in the one case closes or opens an 

 electric circuit, in the other conpensates for the linear expansion of 

 the wheel. Two strips of different metals are usually fastened 

 side by side ; and, as one of them expands faster than the other, it 

 causes the system to bend one way or the other. As an electric 

 current causes heating, and as the amount of heating is proportional 

 to the square of the current, some such arrangement as the above 

 might be used for measuring current strength. The disadvantage 

 with the ordinary form would be that the instrument would have 

 to be adjusted for every change of temperature. To avoid this, 

 Messrs. Geyer and Bristor use a broad strip and a wire of german 

 silver fastened together; one end fixed, the other attached to a reg- 

 istering arrangement. The current passes through these strips in 

 series. Now, while for ordinary changes of temperature both the 

 strip and the wire expand alike, yet, when a current is sent through 

 them, the wire, having the smaller section and less radiating sur- 

 face, heats the faster, and its greater expansion deflects the needle. 

 By a suitable gearing the deflections are made directly proportional 

 to the currents. This instrument can measure both alternating and 

 direct currents. It is simple, and should be unaffected by the pres- 

 ence of magnets. 



The Water-Jet Telephone-Transmitter. — This trans- 

 mitter has been recently exhibited in England, where it has at- 

 tracted attention, both by its novelty, and its excellent performance 

 as a long-distance transmitter. The following is an abstract from a 

 lecture recently delivered by Mr. G. W. de Tunzeemann : " The 

 jet-transmitter consists of a small jet of water, acidulated to ren- 

 der it a conductor, falling upon two electrodes, consisting respec- 

 tively of a platinum wire, and a platinum ring concentric with the 

 wire, and separated from it by a ring of glass or ebonite. The 

 connection between the electrodes is formed by the nappe of the 

 jet ; and, when the jet is thrown into vibration by the sound of the 

 voice, the variation of resistance between the electrodes causes it 

 to act as a transmitter of great delicacy. This delicacy is so great 

 that the voice of a person speaking in an ordinary tone at a dis- 

 tance of fifteen or twenty feet from the instrument is reproduced 

 in a distant telephone with the most perfect distinctness." 



