Page:Popular Science Monthly Volume 45.djvu/646

626 electrical system will be untouched, but the engines will be replaced by motors operated by current from the falls station.

As has been justified by the importance of the subject, there have been some quite exhaustive experiments undertaken by various scientists to determine the frequency of alternation at which unsteadiness of the light from both incandescent and arc lamps is observable or at least objectionable. Several independent experimenters have arrived at results sufficiently satisfactory to themselves, but which unfortunately can not be used as reliable data, for the reason that they are highly discrepant with each other. One reason for this is the evident one of the difference between different makes of lamps, but the discrepancies are of a character not altogether to be explained on that ground. With the ordinary fifty-volt filament, however, it would seem that we may place the working rate of alternation at about thirty or over; with arc lamps, at about fifty or over.

As above mentioned, the arc lighting will be done by making use of the motor transformer (a motor operated by the power current driving a dynamo generating, if we may call it so, the secondary current), but it is expected that by means of a special form of incandescent lamp—the Bernstein, which has, indeed, been on the market for several years—the twenty-five-period current will be available for direct use for illumination by means of incandescent lamps. It is evident that the thicker the filament the longer will its incandescence take to die out (as well as to start up), and a current of twenty-five pulsations, which may not be available for the high-resistance (thin) filament, may be quite sufficiently so for a low-resistance one, which the Bernstein lamp above mentioned is.

The voltage at which the first installation of generators is to operate is somewhat over two thousand. Considering the perfection to which European practice has been carried in the construction of alternating-current machines for much higher electrical pressures than the above, it seems strange that this voltage should have been decided on in a situation where one would expect the very highest degree of perfection to be attained. It is stated, however, that it was largely on account of the comparatively backward condition of that branch of electrical engineering construction in America that the voltage had to be placed so low.

In a case like the present one, where the power station will be under the supervision of skilled engineers, and not merely of men whose chief qualifications are those of sobriety and an ability to stay awake at night, there appears no sufficient reason why the generators should not be operated at five times the voltage named. The fact of the armatures in these machines being fixed gives, moreover, additional security against danger consequent on such