242 



NATURE 



[November 6, 1919 



the last 150 years. Perhaps a review of some of 

 the earlier advances already slipping out of know- 

 ledge, as well as of more recent and familiar 

 discoveries, will be interesting. 



Eighty years ago Dr. Lardner said it was due 

 to the steam engine that reason had taken the 

 place of force, the pen had superseded the sword, 

 and that war had almost ceased on the earth. 

 History does not confirm the prescience of this. 

 The last war, largely an engineering war, owes 

 its vast range and frightful devastation to means 

 placed in the hands of armies and navies by 

 mechanical science. To take one point, success in 

 war depends chiefly on the rapidity with which 

 large masses of men can be moved and served 

 with ammunition and food. This must be accom- 

 plished by railways and motor trucks. At Verdun 

 sixty million shells containing three million 

 tons of steel were expended in thirty weeks. 



During the last fifty years there has been a 

 wide extension of research in mechanical science. 

 Most large engineering works have their labora- 

 tory for testing materials, and the problems in- 

 vestigated are largely those suggested by indus- 

 trial operations. This was specially important 

 during the war, and it is now necessary to make 

 permanent the more intelligent and active spirit 

 thus aroused. 



Hydraulics is a very old subject of research. 

 Its problems are generally too complex for purely 

 rational solution. Hence the need of continued 

 ■experiment. A remarkable series of measure- 

 ments of flow over weirs of different forms, under 

 diff'erent conditions, with varying velocities of 

 approach, and an investigation of the peculiar 

 change of form of the water nappe on the weir 

 crest at low discharges, was communicated by 

 Bazin to the .'Vnn. des Fonts et Chauss^es in 

 1888-98. 



In 1885 Froude gave the first direct determina- 

 tion of the frictional resistance of surfaces of 

 different roughness in water (Brit, .'\ssoc. Report). 

 The most novel result was that the average fric- 

 tion per square foot depended on the length of 

 the surface in the direction of motion. The fric- 

 tion of rotating discs was investigated by Unwin 

 in 1880, and by Gibson in 1910. A research by 

 Stanton and Pannell (Trans. R.S., 1914) has 

 shown the conditions of similarity of motion in 

 fluids, and extended the results to water and air 

 and to high velocities. These results have been 

 of service in discussing the resistance of aero- 

 planes as tested in wind channels. Osborne 

 Reynolds's experiments in 1882 showed that in 

 flow-in pipes there was a critical velocity below 

 which the resistance varied as the velocity, and 

 above nearly as the square of the velocity. 



Froude applied his results to the extremely im- 

 portant subject of the calculation of the resistance 

 of ships. The greater part of the resistance is 

 due to skin friction, and can be calculated on the 

 assumption that the wetted surface is equivalent 

 to a plane of equal area and length in the direc- 

 tion of motion and equal roughness. The re- 

 mainder of the resistance, due to waves and eddies, 

 NO. 2610, VOL. IO4I 



can be found by model experiments. There is 

 an exact relation between wave and eddy resist- 

 ance of the model and ship at corresponding 

 speeds. The method of model tests of ships as 

 a guide to design is now fully established. Sir 

 .Alfred Yarrow has generously established an ad- 

 mirable ship model tank at the National Physical 

 Laboratory. 



Water-power is one of the oldest sources of 

 mechanical energy for industrial purposes. Its 

 importance, looking to the fact of the limitations 

 of coal supply and that in favourable circum- 

 stances it is cheaper than steam-power, can 



' scarcely be over-estimated. Its use has greatly 

 helped processes such as the fixation of atmo- 

 spheric nitrogen, and the production of aluminium, 



I calcic carbide, carborundum, caustic soda, etc., 

 besides being an essential auxiliary in many great 

 electric lighting installations. Thirty years ago 

 no water turbine existed of 1000 h.p. ; now tur- 

 bines up to 20,000 h.p. have been made. T 



j harnessing of Niagara, commenced in 1890, ga' 

 rise to a movement for utilising water-power o' 

 a great scale. The possibility of transmitting 

 energv electrically to distances up to 200 miles, 

 with little loss and commercial success, has 

 greatly enhanced the availability of water-power. 

 In the U.S.A. some seven million horse-power 

 are utilised, in Norway more than one million, 



' in Canada two millions, and in Italy one million. 



, There are great possibilities in the British 



i Dominions. In Canada and some other countri 



1 a Government survey of the water-power 



I sources is in progress. 



In 1869 the steam engine differed little froi 

 what it was as Watt left it, except in detail, 

 size, and variety of application. One important 

 modification since may be noted. Rankine and 

 Clausius drew up a complete rational theory 



i based on the mechanical equivalent of heat. But 

 it appeared that actual engines used 40 to 60 per 

 cent, more steam than was accounted for by the 

 theory. In the late 'fifties Hirn, of Colmar, 

 traced the discrepancv to the conductivity of the 



1 cylinder wall, which was cooled by evaporation 



' to the condenser during exhaust, and then con- 

 densed part of the steam on admission. To 

 remedy this he introduced superheated steam, 

 used to some extent in the 'sixties with economical 

 results, but not widely adopted until the 'nineties. 



; Watt aimed at getting a dry, hot cylinder, but 



\ only partly succeeded. Superheating is a further 



I step, only second in importance to the separate 



I condenser. 



i The greatest change in the generation of power 

 is due to the perfecting of the steam turbine by 

 Sir Charles Parsons. The principle of the steam 

 turbine is old, but it involved great scientific 

 tenacity and courage and large, unremunerative 

 expenditure before practical success was achieved. 

 The first condensing turbine of 100 h.p. was made 

 in 1892. Now in the latest cruiser, the Raleigh, 

 there are turbines of 70,000 h.p. For large elec- 

 tric installations and for large and speedy ships 



. the steam turbine has superseded the reciprocating 



