1920 .] 
Reviews and Abstracts. 
63 
Zealand. The absence at the Chathams of timber large enough to make 
dug-out canoes would be a sufficient motive for the development of these 
elements into a craft of the type described. There are two good figures. 
H. D. S. 
The Edible Fish, &c., of Taupo-nui-a-Tia, by the Rev. H. J. Fletcher. 
Trans. N.Z. Inst., vol. 51, pp. 259-64, 1919. 
The paper gives a brief account of the food fishes eaten by the ancient 
inhabitants of the Taupo district, and of the methods of catching them. 
The Supply of Single-phase Power from Three-phase Systems, by 
Miles Walker, Journal of the Institute of Electrical Engineers , vol. 57, 
No. 278, pp. 109-48, January, 1919. 
The paper deals principally with the supply of single-phase power to 
electric furnaces. The following methods are enumerated :—- 
(1.) Single-phase generators driven by prime movers : 
(2.) Three-phase generators constructed so as to give single-phase power : 
(3.) Motor generator sets : 
(4.) The taking of single-phase current direct from one of the phases 
of a three-phase supply system, and the use of a balancer-— 
stationary or running—for balancing the phases : 
(5.) A rotating balancing transformer which absorbs the balanced three- 
phase power in one winding and supplies a single-phase load 
from an independent winding. 
Running balancers in method (4) are further classified under five 
sub-headings according to the kind of boosting appliance employed, as 
follows :— 
(4 a.) Unsymmetrical number of turns in the balancer winding : 
(45.) Booster transformer in series with the winding : 
(4c.) Addition of choke-coils or condensers to some of the phases : 
(id.) Booster generator in series with the winding : 
(4c.) The generator of an oppositely rotating magnetic field of double 
the frequency. 
The main objection to the first method is that the cost of a single-phase 
generator for a given ou put is higher than for a three-phase generator— 
in the case of a 5,000 kw., 25-cycle, 1,500-revolution machine about 30 per 
cent, higher. 
In the second method it is established that if the single-phase load 
(even of low power-factor) does not exceed 20 per cent, of the normal three- 
phase load the disturbance to the voltage is inconsiderable. 
In the third method the motor generator may consist of an induction 
motor direct-connected to a single-phase generator, or a synchronous motor 
may be used in place of the induction motor. For general convenience 
of operation this method is entirely satisfactory, the main drawback being 
the high first cost and poor over-all efficiency. 
In the case of stationary apparatus, used in method (4), it is pointed 
out that if left always in circuit the condenser or choking-coil will produce 
as much out of balance when the furnace is not taking current as the 
furnace produces when no compensation is employed ; and, although 
automatic gear for switching is possible, such automatic arrangements are 
not looked upon with favour by electrical manufacturers. 
The same objection applies to running balancers, under subdivisions (a) 
and (5). 
The advantage of method (c) over the boosting transformer method 
is that the injected voltage in the choke-coil rises automatically with the 
