November 6, 19 19] 



NATURE 



243 



engine. Lately Sir Charles Parsons has intro- 

 duced gear for reducing the necessarily high tur- 

 bine speed to one more suitable for the propeller, 

 and this will much extend the use of the turbine 

 in marine engineering. . 



The development of the internal-combustion 

 engine belongs almost entirely to the last half- 

 century. On it has depended all aircraft and sub- 

 marines, and most mechanical road transport. 

 The first satisfactory gas engine was that of Dr. 

 Otto in 1876. Dowson, in 1878, introduced pro- 

 ducer gas, emancipating the engine from depend- 

 ence on illuminating or town gas ; and Benier 

 soon after invented the suction producer. The 

 Germans developed the large-cylinder, high- 

 powered gas engine chiefly for utilising blast- 

 furnace and coke-oven gas — a waste product. Sir 

 Dugald Clerk, who has led the way in this country 

 in developing the gas engine, and especially in 

 studying its theory, estimates that there were 



of 



million h.p. at work 



gas engines 

 1909. 



The first paraffin engine was that of I'riestman 

 in 1885. The Diesel oil engine, introduced in 

 1893, has perhaps the greatest thermal efficiency 

 of anv heat engine. 



The petrol engine, which has made the con- 

 quest of the air possible, was greatly im- 

 proved during the war, and is the lightest of 

 heat motors. .\n aeroplane engine of 850 h.p. is 

 stated to weigh only 1-63 lb. per h.p. 



The future of air transport has verv great 

 promise, but it looks as if for commercial purposes 

 the airship has advantages over the aeroplane. 

 In coastal patrol and anti-submarine work naval 

 airships carried out 9000 patrols covering 

 i\ million miles. Engineers interested believe 

 that an airship capable of carrying 1000 persons 

 at 80 miles an hour is in reach of present prac- 

 tice. .Attempts are being made to produce helium 

 to replace hydrogen in the envelope, removing 

 one .source of danger. 



-Mr. Lanchester has reminded us that, with 



Government help largely withdrawn, the aerp- 

 nautical industry is in the position of a youth 

 luxuriously brought up who finds himself face to 

 face with the fact that he has to earn his own 

 livelihood. 



.Structures and machines should be designed 

 with adequate strength and at the same time with 

 the least necessary material. In the old view the 

 strength limit was the statical breaking weight, 

 and the ratio of this to the working stress was 

 termed the factor of safety. Wohler's research 

 in 187 1 proved that, in ordinary conditions of con- 

 tinual variation of stress, fracture occurred with 

 much less than the statical breaking weight, and 

 depended on the range of variation of stress. 

 Bauschinger showed that the position of the elastic 

 limit changed with repetition of straining action, 

 and that the range of elasticity appeared to be 

 the same as the range of stress, which could be 

 .sustained indefinitely. Bairstow and Stanton have 

 confirmed this. Osborne Reynolds constructed a 

 machine in which continuous changes of stress 

 in a test bar could be produced by the inertia of 

 reciprocating weights. 



In the period under consideration there has 

 been a great extension of public and private 

 mechanical testing laboratories. The National 

 Physical Laboratory and the Bureau of Standards, 

 Washington, are now (iovernment institutions. 

 In the U.S.. A. very large testing machines have 

 been constructed, several of 600 tons capacity, 

 and one of 5000 tons at Pittsburgh. For testing 

 full-size members such as bridge ties, reinforced 

 concrete columns, etc., such machines are neces- 

 sary. Though new tests of materials must be 

 adopted with great caution, tests of hardness and 

 tests of brittleness have been found useful. 

 Guest, Scoble, and others have investigated 

 compound stress, and found that in ductile 

 materials the limit of resistance is the greatest 

 shear stress. .\ very great advance has been 

 made in the delicacy and accuracv of strain 

 me.'isuring instruments. 



THE TREND OF MODERN METALLURGY. 



Bv Prof. H. C. H. Carpemkr, F.R.S. 



A/T inWLLURGY Is the art of extracting metals 

 •^ ' -•• from their ores, refining them, and working 

 them up into finished products for the use of man- 

 kind at a profit. The inevitable corollary of this 

 is that the economic factor is always decisive as 

 to the applicability or otherwise of any new scien- 

 tific discovery which bears upon the industry. 

 The art is one of the oldest in the world, but in 

 spite of its highly diversified character and the 

 profound influence that scientific methods have 

 had upon its scope and technique, it does not 

 differ to-day in essence from the -ancient art 

 except in the fact that to an ever-increasing extent 

 the applications of science are found to be pay- 

 able. 



In attempting a survey of the present position 

 NO. 2610, VOL. 104] 



and tendencies of the great metallurgical indus- 

 tries, only the broadest treatment is possible. 

 .Accordingly, no account will be taken of the usual 

 subdivision of the subject into ferrous and non- 

 ferrous metallurgy. Rather does there appear to 

 be an advantage in omitting this distinction which 

 has no scientific basis, but is purely one of 

 custom. 



The first stage in the passage from the mineral 

 as mined to the manufactured metal is "ore- 

 dressing," and here a very notable advance, made 

 in the last few years, has to be recorded. The 

 old method of "gravity " concentration, whereby 

 the ore after being crushed was suspended in 

 water and treated in a variety of machines for 

 the concentration of the metallic contents, which. 



