404 REPORTS ON THE STATE OF SCIENCE, ETC. 
as experience may show that the yield is either greater or less than has been 
anticipated ; if the latter, unnecessary expenditure may have been incurred. 
2. The hydro-electric works which have been constructed give an 
opportunity of recording the yield from catchment areas, and such informa- 
tion is helpful i in dealing with adjacent catchments of similar character. 
3. It is customary for the hydro-electric companies to prepare a balance- 
sheet of the rainfall and of water utilised and lost. The following informa- 
tion is usually recorded :— 
(a) Year. 
(b) Average rainfall on catchment area in inches. 
(c) The level of the water in the main reservoirs on January 1. 
(d) The increase or decrease of storage water during the year. 
(e) Water lost over the spillway of dams as measured by continuously 
recording water level gauge. 
(f) Losses from any subsidiary catchments not flowing directly to the 
main reservoirs, or water run to waste. 
(g) Water utilised for power as measured over weirs or through Venturi 
meters. 
(h) Total available water. 
(2) Total water accounted for. 
(j) Loss due to evaporation, absorption, etc., i.e. the difference between 
(h) and (2). 
By means of these balance-sheets the yield from the catchment area is 
obtained, and, by measurement of exceptional increase in the rate of rise of 
water in the reservoirs, intensities of inflow owing to flood conditions and 
melting snow can be calculated ; should the reservoir be full when such 
flood conditions occur the record of the flow over the dam spillway would 
also give a measure of the flood conditions. 
4. I believe that the hydro-electric companies would be willing to give 
information of the yield of catchment areas to a central authority. It is 
possible that existing systems of recording data may require modification 
to bring them into accord with any recommendations of a central authority. 
Sus-MEmoranDvuM D (4). 
ELECTRICITY STATIONS. 
By Henry Nimmo. 
There were 454 stations owned by authorised electricity supply under- 
takers in operation at the end of 1932, against 483 in 1931 and 511 in 1930. 
With the coming into operation of the grid the decrease will be more rapid 
in the next two or three years, until only about 120 selected stations are left 
to generate all the electricity required by authorised electricity supply 
authorities. 
In addition there were, at the end of 1932, 50 (against 55 in the previous 
year) stations owned by railway, tramway and certain non-statutory bodies, 
and there are still a large number in factories, mines, etc. "The number 
of these, however, is expected to decrease rapidly when the full effect of 
the grid scheme takes place. 
At the end of 1932 there was installed in the stations of authorised under- 
takers over 7 million kw. of plant, of which nearly 97 per cent. is steam 
driven, the remainder having oil and gas (about 2 per cent.) and over 1 per 
cent. water-driven prime movers. 
The maximum load on the stations of authorised undertakers was of the 
order of 4 million kw., and 12,225 million kilowatt-hours were generated 
during the year, the load factor approaching 35 per cent. 
