SCIENCE AND INDUSTRY. 
scale are being dealt with. The design of economical furnaces, the 
‘selection and preparation of suitable refractories, are but two of the 
dines along which this research has been directed. 
The last of the departments of the Laboratory is the William Froude 
National Tank. This consists of a basin 500 feet long, 80 feet wide, 
and 12 feet 6 inches deep in the middle. It is spanned by a travelling 
platform or carriage, which runs on accurately levelled rails, being pro- 
pelled by four powerful motors. By means of these, the carriage can 
be brought up to any required speed (up to about 20 miles an hour) 
quite rapidly, and the desired speed maintained for quite “a large por- 
tion of the travel of the carriage. The carriage tows a scale model of 
the ship whose design is under test, and from the resistance to. towing 
at various speeds, which is measured by dynamometers on the carriage, 
information-as to the performance of the full-sized ship can be ob- 
tained. The model is towed at much lower speeds than those at which 
the ship will be driven, the relations between speeds, resistances, and 
linear dimensions being known by the application of the principles of 
dynamic similarity. Quite recently the lines of a tramp steamer were 
investigated, and from the results of tests on the model improvements 
were suggested which resulted in a reduction of 35 per cent. in the 
horsepower required to drive the steamer. 
Very large use was made of the tank during the war, but of this it 
is wiser to say too little than too much. However, we may quote a 
statement that has been published, to the effect that Sir Alfred Yarrow 
credited the staff of the tank with having drawn out the lines of the 
world’s fastest. destroyer. ; 
Acknowledgments are made to Dr. Rosenhain for extracts from his 
lecture before the West of Scotland Iron and Steel Institute; for 
plan of National Physical Laboratory to National Physical Laboratory 
circular letter; and for photos. to National Physical Laboratory staff. 
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