HYDRO ELECTRIC INSTALLATIONS. LXIIl. 
tail race of considerable dimensions. But even for low 
head falls where the hydraulic works have to be on a 
considerable scale to deal with a large volume of water, 
the hydro electric power house is immensely superior to a 
steam power station, as there is no chimney, boiler house, 
coal store, pump room, etc. The building is merely a 
simple shell of considerable length compared with the 
width. The Oakland power house for example is 275 feet 
long by 40 feet wide, and that for the Snowdon trans- 
mission 145 feet by 40 feet. 
The switchboard is usually situated in a room midway 
along one side, and it has over it the tower from which 
the transmission lines lead away. Step up transformers 
are sometimes placed underneath the switchroom, but it 
is well to locate them in an entirely separate building 
because of the oil. At Niagara a canal divides the 
transformers from the power house. 
The attendance required in a hydro electric station is 
remarkably low, an average of many stations giving it at 
less than one fourth of what is necessary with steam. — 
As the combined cost of fuel and labour in a steam station 
is $lbs. of the total, it will be seen what a great saving 
water gives. 
Water Wheels.—In a general way it may be said that 
impulse wheels are used for heads of over 400 feet, and 
turbines for under that. The Pelton or impulse wheel in 
which the water impinges against a part only of the 
periphery has the advantage over a turbine of being very 
cheap; indeed it is the cheapest form of prime mover. 
It is also able to work with any head; in one case in 
Mexico over 2000 feet being employed. With such high 
heads the buckets wear out quickly, and it is necessary to 
go to the trouble of building forebays, etc., to allow sand 
and other solid matters to settle. 
