[J. F. I.
be induced high frequency current of an a m o u n t so that a thermometer under the arm would register IO5 ° F., an artificial fever, so to speak. Shoulder bursitis can often be traced to some harmful local exertion. A painful " s t i f f " shoulder results and the arm m a y become almost completely useless. An X - r a y may disclose a lime deposit near the bone. Until a few years ago it was best practice to remove the deposit surgically. It now looks as though operation for bursitis might seldom, or never, be necessary. One case of bursitis studied was t h a t of a man who had indulged in more physical exercise than usual. T r e a t m e n t s with the high frequency apparatus eliminated the pain and the deposits as shown b y the X-ray. Another case was that of a woman who had had a troublesome shoulder for ten or more years. This was also eliminated. Dr. W h i t n e y points out that while heat application has been employed successfully in such cases b y various means, it does not necessarily follow that the action is simply one of dissolution of solids brought about by the warmer plasma. Other v e r y interesting questions are discussed b y Dr. Whitney from the point of view of research such as deposits in the arteries and the suggestion of a possible reaction to reduced temperature. R. H. O. S w e d e n Builds a P u m p e d - S t o r a g e Plant.--(Power, Vol. 79, no. 3) GEORGE WILLOCK, engineer at Trollh~ittan, Sweden, describes the plant at Sillre on the Indal River, 40 miles up from the Gulf of Bothonia. T h e plant operates in combination with Norrfors hydro-electric system of 22,000 kw. capacity on the Umea River, I5O miles north of Sillre. A reservoir cannot be created at Norrfors, so surplus power during off peak periods is transmitted to Sillre to pump water to a storage reservoir 640 ft. above river level, whereby an additional 5,000,000 kw.h. is obtained for peak service. This reservoir has a useful storage capacity of 706,000,000 cu. ft. Water is brought to the power house through an unlined tunnel 7,500 ft. long and of 176.6 sq. ft. cross section and a penstock 3,o5I ft. long by 6 ft. diameter. The power house is designed for three units, but only one, rated at 6o00 kw. has been installed. T h e pump is a two stage centrifugal type with a capacity of 30,000 to 45,000 g.p.m, against a head of 745 to 600 ft. at a speed of 600 R.P.M. T h e turbine will develop lO,O8O hp. under a maximum head of 656 ft. T h e 3-phase alternator rated at 50 cycles has a direct coupled exciter. When operating as a motor its o u t p u t is 7000 kw. at unity power factor. All are connected on one vertical shaft.
Pump test results showed a maximum efficiency of 86 per cent. with discharge of 41,2oo g.p.m, against 656 ft. head. A maximum water wheel efficiency of 91.6 per cent. was obtained at about 0.9 rated load and 554 ft. head. R. H. O. Stationary Commutator D. C. Motor.--In a paper by Dr. E. F. W. ALEXANDERSONAND A. H. MITAGG presented at the A. I. E. E. winter convention there was announced the development of the Thyratron motor which has series direct current characteristics and operates on alternating current. It was made possible by recent advances in electron tube applications. One such motor is now on test. It is rated at 400 hp. 625 r.p.m., and 75 hp. at 350 r.p.m., and is intended for driving an induced draft fan. The motor speed may be controlled down to a standstill. It operates from 2300 v., 3phase, 6o-cycle power and has a stationary armature and revolving field. The electron tubes perform commutation and grid-controlled rectification, the latter providing continuous power control from standstill to maximum speed. R. H. O.
A New Source of "Kilocycle Kilowatts."--L. D. MILES, in an article in Electrical Engineering for March I935, explains how electric power at frequencies of I,OOOto IOO,OOOcycles per second is obtained at low cost by means of an electronic tube known as the arc tube. The arc tube consists essentially of two electrodes closely spaced in inert gas under high pressure. A general-purpose circuit consists of a choke coil, a stabilizing resistor, a capacitator and an inductor in series. The tube is connected across the capacitator and the inductor, and the output at any desired voltage may be taken from the secondary of a transformer which constitutes the inductor. In high power applications the stabilizing resistor may take the form of the ohmic resistance of the windings of an electromagnetic field. The cycle of operation is as follows. When voltage is applied, the capacitator is charged through the resistor, the choke causing a momentary pause in the starting cycle. When the capacitator is charged to the breakdown voltage between the tube electrodes, the tube ionizes, acts as an instantaneous short circuit, and allows the capacitator to discharge th rough the inductor-capacitatortube circuit. Line current inrush is prevented by the choke. At the instant the capacitator is completely discharged, a high current is flowing in the inductor-capacitator-tube circuit. The inductor continues current flow, which overdischarges the capacitator and drives the tube voltage negative, whereupon the arc extinguishes