February 25, 1909] 



NA TURE 



503 



be some better solution of the problem, and doubtless he 

 made many experiments before he realised the true solu- 

 tion in a condenser separate from the cylinder of the 

 engine. It is easy after discovery to say how obvious 

 and how simple, but many of us here know how diflicult 

 is any step of advance when shrouded by unknown 

 surroundings, and 1 can well appreciate the courage and 

 the amount of investigation necessary before James Watt 

 thought himself justified in trying the separate condenser. 



But to us now, and to the youngest student who knows 

 the laws of steam as formulated by Carnot, Joule, and 

 Kelvin, the separate condenser is the obvious means of 

 constructing an economical condensing engine. 



Watt's experiments led him to a clear view of the great 

 importance of securing as much expansion as possible in 

 his engines. The materials and appliances for boiler con- 

 struction were at that time so undeveloped that steam 

 pressures were practically limited to a few pounds above 

 atmospheric pressure. The cylinders and pistons of his 

 engines were not constructed with the facility and accuracj 

 with w-hich we are now accustomed, and chiefly for these 

 reasons expansion ratios of from two- to three-fold were 

 the usual practice. Walt had given to the world an engine 

 which consumed from five to seven pounds of coal per 

 horse-power hour, or one-quarter of the fuel previously 

 used by any engine. With this consumption of fuel its 

 field under the conditions prevailing at the time was prac- 

 ticallv unlimited. What need was there, therefore, for 

 commercial reasons, to endeavour still further to improve 

 the engine at the ri!.k of encountering fresh difficulties and 

 greater commercial embarrassments? The course was 

 rather for him and his partners to devo'.e all their energy 

 to extend the adoption of the engine as it stood, and this 

 they did ; and to the Watt engine consuming from five to 

 seven pounds of coal per horse-power mankind owes the 

 greatest permanent advances in material welfare recorded 

 in history. 



The Watt engine, with secondary modifications, was the 

 prime mover in most general use for eighty years until 

 the middle of the last centurv, when the compound engine 

 began to be introduced. Why, we may inquire, was it 

 that the compound engine was so long in coming into 

 use, for it had been patented bv Hornblower in 17S1, or 

 seventy years before? and why does John Bourne in his 

 large book, " Practical Instructions for the Manufacture 

 and .Management of every Species of Engine," published 

 1872, make no mention in the index of the compound or 

 triple expansions, and when he speaks of Hornblowcr's 

 double-cylinder engine (really a compound engine) does he 

 do so in disparaging terms, mentioning that there was no 

 increased economy in steam over the single cylinder? This 

 last statement provides an answer to our inquiry, for it 

 is correct in view of the very low steam pressure in general 

 use before that time, or until somewhat before the middle 

 of the last century, when the introduction of the loco- 

 motive led to a general rise in pressures on land, and the 

 surface condenser some years later to increased steam 

 pressure at sea. Also, we must remember that many 

 experiments have shown that unless the mean difference 

 of pressure on a piston exceeds about 7 lb. per sq. inch, 

 the friction, the bulk, the momentum of the moving parts, 

 and the cost make such a cylinder not worth having. The 

 case, however, with the turbine is entirely different, and 

 it is chiefly owing to this difference and to its power of 

 usefully expanding the steam down to the very lowest 

 vapour pressure attainable in the best condenser that it 

 has surpassed the best reciprocating engines in economy of 

 steam. To return to our subject. The introduction of the 

 compound, triple, and quadruple expansion engines was 

 therefore concurrent with the improvements in boiler con- 

 struction, the introduction of the surface condenser, and 

 the general rise in steam pressure, and by the quadruple 

 engine the expansion ratio has been extended up to about 

 sixteen-fold, and the consumption of coal per horse-power 

 reduced to from i| lb. to ij lb. per horse-power hour, or 

 to from one-fourth to one-third the fuel consumed in the 

 time of James Watt. Let us now direct our attention to 

 the turbine engine, which derives its power, not from the 

 pressure of the steam on a piston, but from the momentum 

 of the steam at high velocity curving around and blowing 

 forward the vanes or paddles attached to the shaft. 



NO. 2052, VOL. 79] 



It is unnecessary here to recapitulate the many attempts 

 to construct a successful steam turbine from the days of 

 Hero until a quarter of a century ago, as several excellent 

 books are now published on the subject. It is true that 

 the difliculties of construction and inferior workmanship 

 available during this early period were a serious bar to 

 progress, but the chief bar to progress lay in the fact that 

 the turbine, to be economical in steam, must (at least 

 in its primitive form) rotate at a very high . speed, and 

 that before 1880 there was no commercial use for such 

 a high-speed engine excepting through the intermediary of 

 belts or friction gearing, or for such e.xceptional purposes 

 as the direct driving of circular saws. The chief purpose 

 for which turbines are now extensively used on land did 

 not then exist, namely, for the driving of dynamos. Then, 

 again, belts for high speeds are a very unsatisfactory 

 appliance, and accurately cut spiral gearing as recently 

 introduced by Dr. de Laval had not been devised ; and, 

 again, the problem of applying a turbine to the propulsion 

 of vessels being surrounded, as it was, with great con- 

 sequential difficulties would naturally only be attacked 

 after the successful application of the prime mover to some 

 easier and simpler purpose on land, so that I think, on 

 the whole, we may safely say that under the conditions 

 prevailing the commercial introduction of the turbine before 

 1880 was a practical impossibility. 



It is a matter of history that the turbine principle had 

 been used for obtaining power from waterfalls before the 

 days of James Walt, but I am not clear that he had in 

 mind any concrete form of steam turbine ; yet in 1770 he 

 suggested " a circular engine consisting of a right-handed 

 and left-handed bottle-screw spiral involved in one another," 

 and he also appears to have had a leaning towards some 

 form of directly rotary engine, for in 1769 he took a patent 

 for a Barker's reaction water-wheel, the water pressure 

 being derived from the action of steam on water, as in 

 Savery's fire-engine or a modern pulsometer. He also 

 designed a rotary abutment engine in 1782, but in none 

 of these machines is there any indication of an attempt 

 to gain greater expansion ratios for the steam. 



It is peculiarly interesting to recall on this occasion 

 that one of the earliest steam turbines to be put to prac- 

 tical work was in this town ; it was about the middle of 

 the last century, and was a turbine like that described by 

 Branca in 1629. It consisted of a steam jet playing upon 

 a paddle-wheel, coupled to a circular saw, which it drove 

 for some years. The principle of the expansive working 

 of steam was, however, only to a small extent utilised in 

 this engine, for I believe that the steam jet was non- 

 divergent, which implies a useful expansion ratio of only 

 about ij-fold. One of the most conspicuous workers in 

 the design of the compound turbine was Robert Wilson, 

 of Greenock, Master of Arts of Edinburgh, who lodged a 

 patent in 1848. This patent was of unusual length and 

 wealth of detail, and describes radial-flow and parallel- 

 flow compound turbines, designed for moderate ratios of 

 expansion. The blades and guides were proposed to be 

 fastened by casting them into the hub and case, a method 

 occasionallv used at the present time. 



The principles of Wilson's design are generally correct, 

 but the proportions of his turbines are extravagantly in- 

 correct, the blades being too large and too few for success. 

 I had a model made of Wilson's turbine eighteen years 

 ago, and under steam all that could be said was that it 

 went round the right way. I do not think that Wilson 

 can have made a model and tested it before he applied 

 for his patent, the course followed by James Watt, and 

 one which is to be strongly recommended to the attention 

 of inventors generally in' almost all circumstances, as 

 saving time, money, and disappointment. There have been 

 manv workers on steam turbines of English nationality 

 before and since the time of Wilson, but within the last 

 twenty years other countries have taken up the subject with 

 zest. 



Prior to 1880 the uses for a very high-speed motor were 

 few, as we have seen ; the speed of revolution of steam 

 wheels, as Bourne described them in 1872, " was incon- 

 venientlv high for most purposes," but after 1880 con- 

 ditions w-ere changed : the beautiful machine, the milk 

 separator, of Dr. de Laval, of Stockholm, and the great 

 invention of the dvnamo electric machine had come, and 



