484 



NATURE 



[March 22, 1894 



consisted of Lord Kelvin (then Sir William Thomson) 

 as president ; Dr. Coleman Sellers, of Philadelphia ; 

 Prof. E. Mascart, Paris ; Colonel Theodore Turrettini, 

 Geneva; and Prof. W. Cawthorne Unwin, F.R.S., as 

 .zficretary. Funds were placed in their hands for the 

 purpose of paying a fixed sum to each competitor send- 

 ing in a scheme of sufficient importance, and awardmg 

 prizes. Meetings of the commissioners were held in 

 London, but no decision was come to as to whether 

 compressed air or electricity should be used — the two 

 means of distributing the power for which schemes 

 were submitted, — and they were not convinced of 

 the superiority of an alternating current over a 

 continuous current system of electrical distribution. 

 Since the commission dissolved, however, a decision 

 was come to in favour of the adoption of electrical 

 distribution, and Prof. George Forbes, F.R.S., being ap- 

 pointed electrical consulting engineer, the outcome has 

 been the adoption of the scheme originally submitted to 

 the commission by him in 1890 and rejected at the time 

 by every one of the commissioners. In that scheme it 



in the continuous current system to increase the pressure 

 to the figure necessary for economical transmission), and 

 the admirable facility with which the alternating current 

 can be reduced from high to low pressure, and vice versa, 

 for the various requirements — such as electric traction, 

 electrometallurgy, motive-power and lighting — ^by that 

 machine which does its work without mechanically 

 moving parts — the alternating current transformer — are 

 strong points in favour of the use of alternating currents. 

 The question of motors is, on the other hand, a strong 

 one, ordinarily, in favour of continuous cuirents. But 

 when the frequency of the alternating current is low, as 

 is to be the case at Niagara Falls, most of the advantages 

 of continuous current motors over alternating current 

 motors disappear, and the operation of many alternating 

 current motors, already existing, is facilitated. ■ ' « 



In regard to the frequency of alternation of the currents 

 to be adopted at Niagara Falls, we find a very marked 

 departure from existing practice. The frequency hitherto 

 used has been from 70 to 100 periods per second in 

 Europe, and 133 in America. There is an exception — 



Fig. 3. 



was insisted that alternating currents must be used, that 

 the two-phase system should be adopted (that is, one 

 •employing two currents which differ from each other with 

 respect to time by 90 degrees or a quarter of a complete 

 period of alternation — when one has a maximum value, 

 positive or negative, the other is a zero, and vice 

 versa), that, using only machinery on the market, 

 2000 volts should be the pressure for local work, 

 and step-up transformers be employed for raising the 

 pressure for transmission to Buffalo (eighteen miles dis- 

 tant), and that the motors for converting the electrical 

 power into mechanical power at the far ends of the lines 

 should be synchronising motors, Tesla two-phase motors, 

 and motors with commutators and laminated fields. This 

 briefly describes the system to be now adopted ; and it is 

 interesting to note the conversion of the commissioners 

 appointed by the Cataract Construction Company, with 

 one notable exception, to viewing with favour the adoption 

 of the alternating current in preference to the continuous 

 current. But the difficulties connected with the insula- 

 tion of the dynamos from the earth, which is necessary 

 when using a number in series (an arrangement required 

 NO. 1273, VOL. 49] 



that of Messrs. Ganz and Co., of Buda-Pesth— who'have 

 adopted 42 periods per second. But the frequency to be 

 used at Niagara Falls will eclipse all, inasmuch as it is 

 to be one of 25 periods per second ; and it may be re- 

 marked here that one of 16 periods per second would 

 have been adopted, had not the weight of the machine 

 for this periodicity been too heavy for the hydraulic 

 piston (which supports the whole weight of the revolv- 

 ing parts of the turbine and dynamo, and the shaft con- 

 necting them, using the head of water driving the turbine, 

 the thrust-bearing shown in Fig. i being merely for pre- 

 venting motion vertically), using the induction in the 

 iron desired by the manufacturers of the machines, which 

 is lower than that which the Cataract Construction Com- 

 pany's electrical consulting engineer would have preferred. 

 The advantages to be derived from the use of so low 

 a rate of alternation are many. One has already been 

 mentioned here, namely, the increased number of alter- 

 nating current motors which become available for use, 

 to which may be added the further great advantage of 

 an improved efficiency in the motors. But probably the 

 greatest advantages of a low frequency are to be found 



