G.—ENGINEERING 133 
to be raised and the power output per unit of weight greatly increased. 
At the present day engines are made of a vast number of different types, 
two- and four-cycle, single- and double-acting, vertical and horizontal, 
each meeting a particular set of conditions in service. Starting by com- 
pressed air is still the most usual method, being universal in the case of 
large engines. For traction purposes, however, and for the smaller 
stationary sets, electrical and mechanical methods now receive increasing 
attention. 
There is boundless scope for the application of the Diesel engine, both 
actual and potential. Its low initial cost, the limited space required for 
its installation, the ease of starting from cold, and its low costs of operation 
and maintenance, are all contributory to its great industrial exploitation, 
particularly for such public services as water and electricity supply, 
sewage and drainage, apart from industrial application. For marine 
purposes the Diesel engine is making steady progress in its adoption for 
the main propelling machinery. With its convenience and reliability 
for auxiliary purposes it is so widely appreciated as to require only passing 
mention here. Examples of this type of plant are to be seen in many 
modern passenger ships. The recent development of a high-speed 
engine, combined with small size and low specific weight, make this 
engine particularly suitable in railway work for locomotives, where low 
operating costs and low standby losses are essential. This is a sphere 
into which the Diesel engine in our country has only recently entered, but 
its singular suitability for this type of service encourages one to expect 
rapid strides to be made in this direction. So far as industrial road 
vehicles are concerned, this type of oil engine has come to stay, while its 
resiliency of running has permitted its installation in crowded residential 
areas—even in the basements of steel structures consisting of flats, where 
freedom from noise and vibration are imperative. There seems, indeed, 
to be no limit to the sphere of utility—of necessity, even—for this prime 
mover. . 
The centrifugal pump is also largely a development of the period under 
review. As is frequently the case, the principle was known long before 
it was applied successfully to practical uses. There is evidence that 
Leonardo da Vinci, the great artist, engineer and inventor, realised the 
possibility of utilising centrifugal force for raising water, though the 
invention of the centrifugal pump is usually attributed to Johann Jordan. 
So far as known records go, centrifugal pumps began to be used for 
industrial purposes in the second decade of last century ; but at the time 
of the Great Exhibition in 1851 they were still regarded as a mysterious 
novelty. One shown by Appold at this exhibition created much interest 
because its impellers would pass an orange, this being one of the first 
steps in an important modern application of this pump, that of dealing 
with solid materials. For a long time the centrifugal pump could not 
compete with that of the plunger type for the greater pressures and heads, 
its efficiency falling off rapidly in the higher ranges, so that its use was 
confined chiefly to low lifts. When Osborne Reynolds’s patent was 
disclosed in 1875 the multi-stage turbine centrifugal pump appeared, and 
the use of guide vanes was found greatly to improve the hydraulic 
