244 



SCIENCE. 



[Vol. XVI. No. 404 



and all its accompanying- vices? Will the poet's dream 

 come true? — 



"Men, my brothers, men the workers, ever reaping something 

 new: 

 That which they have done but earnest of the things that they 

 shall do: 



" For I dipt into the future, far as human eye could see, 

 Saw the Vision of the world, and all the wonders that would be ; 



" Saw the heavenp fill with commerce, argosies of magic sails. 

 Pilots of the purple twilight dropping down with costly bales ; 



" Heard the heavens fill with shouting; and there rained a ghastly 

 dew 

 Prom the nations' airy navies grappling in the eternal blue ; 



' ' Far along the world-wide whisper of the south wind rushing 

 warm. 

 With the standards of the peoples plunging through the thunder- 

 storm ; 



" Till the war-drum throbbed no longer, and the battle-flags were 

 furled 

 In the parliament of man, the federation of the world. 



"There the common sense of most shall hold a fretful realm in 

 awe. 

 And the kindly earth shall slumber, lapt in universal law." 



Whether these things will be realized we know not. In 

 view of the past, we dare not say our wildest dreams and 

 fancies will not to-morrow be realities. But this we know : 

 that wherever it is possible to beuefll mankind, to alleviate 

 suffering, to elevate humanity, and to raise man mote nearly 

 to the true image of his Maker, there the aid of natural sci- 

 ence will never be found wanting. 



THE SECOR SYSTEM OF MARINE PROPULSION. 



Foe over four years there has been in process of development in 

 the city of Bi-ooklyn a system of propelling vessels which it is be- 

 lieved will offer distinct advantages over the marine steam-engine. 

 The following is a brief description, condensed from "General 

 Information Series," No. VIII., of the United States Navy Depart- 

 ment, for 1889: — 



" The propulsion of vessels by the liberation of a large volume 

 of gas by explosion and the displacement of water thereby has 

 been tried, and has met with some success. 



" The method employed is the invention of Mr. Secor. and is 

 fitted to a vessel 100 feet in length, called the ' Eureka.' 



"The apparatus consists of two horizontal tubes about twenty 

 inches in diameter, placed fore and aft io the after part of the 

 vessel below the water-line, the after ends being in communica- 

 tion with the sea. Petroleum in the form of spray, and air under 

 pressure, are injected into the tubes at the forward ends, and ex- 

 ploded by electricity. The disengaged gas expels the water from 

 the tubes, and the reaction against the forward ends of the 

 tubes propels the vessel. The explosions are arranged to take 

 place alternately in the cylinders, and the firing mechanism to 

 work automatically. Sixty explosions a minute in each cylinder 

 have already been obtained, giving quite a uniform motion." 



In 1824 Sadi Carnot propounded the great principle that the 

 useful effect of any heat-engine was independent of the nature of 

 the working fluid, and depended solely on the extremes of tem- 

 perature in the working cylinder; or, as it has been expressed, it 

 depends on the range of temperature of the working fluid during 

 its working cycle. Sir William Thomson determined the exact 

 expression for this efficiency, and it was also deduced analytically 

 by Rankine as follows; — 



T 

 T' is the temperature above the absolute zero at which heat is 

 supplied; and T'', that at which it is rejected. 



In the "Encyclopaedia Britannica" (edition of 1889), article 

 "Steam-Engine," Professor I. A. Ewing points out that in the cylin- 

 der of a gas engine the efficiency would be 87 per cent, if it were 

 possible to expand down to atmospheric temperature and dis- 

 pense with a water-jacket : thus in Centigrade temperature, 

 3173''-388'' 



— ^3172° ~ nearly. 



This would represent an efficiency six times greater than the 

 most economical triple expansion steam-engine. 



The conditions which are impossible in any cylinder containing a 

 moving piston are obtainable by the Secor therm o-dynamic method. 

 The necessity for the wasteful water jacket at once disappears. 

 The degree of expansion with its concomitant fall of temperature 

 is only limited by the temperature of the sea, which constitutes 

 the thermo-dynamic cold body or refrigerator. It may be re- 

 marked that the discharged gases, consisting principally of air, 

 nitrogen, and carbonic acid, are poor radiators of heat, thus limit- 

 ing antecedent heat- waste. 



The conditions of the Secor cycle are, then, an explosion or 

 combustion at the highest temperature —the dissociation limit — 

 within a heated chamber, from which the outflow of heat may be 

 prevented by suitable linings, the non-radiating products of com- 

 bustion expanding in re- action against the coldest medium pro- 

 vided by nature. (the ocean); the cooling being coincident with, 

 and not antecedent to, the mechanical effect. 



Science is to-day making demands of the steam-engine which it 

 can never satisfy. Science says, let no heat escape from smoke- 

 stack, or radiate from boiler, steam-pipe, or cylinder; then increase 

 the range of temperature four or five fold that of the quadruple- 

 expansion steam-engine. Hitherto the reply of the engineer has 

 been, that, inasmuch as no conversion of energy can occur with- 

 out some loss, even 85 or 90 per cent is, after all, not too great a 

 tribute to pay to nature. 



Thurston shows that the cannon does much better, yielding 

 nearly 50 per cent of thermo-dynamic efficiency. The electrician 

 working in a new field, undeterred by precedent, guided only by 

 a knowledge of the laws which relate to the conservation and 

 correlation of energy, has accomplished still greater results. An 

 efficiency of 90 per cent in the dynamo is one of the grandest 

 achievements of applied science. 



Although the method of propulsion in the Secor system involves 

 a radical change as compared with the screw, it is not impossible 

 to estimate the efficiency of an air-jet under the circumstances 

 indicated. The limited area of a jet of air or water has been sup- 

 posed to involve a great loss of efficiency. This idea has arisen 

 principally from erioneous conceptions in respect to the screw. 



It was at one time an axiom in engineering, that the larger the 

 exposed area of the screw, the more effective would be its action. 

 Experience has shown the fallacy of this idea. Data of the trials 

 of three large transatlantic steamers, showing the comparative 

 merits of large and small screws under similar conditions, are 

 given by Arthur I. Maginnis, Esq., in a paper read before the In- 

 stitution of Naval Architects. He remarks, that " by these results 

 it will be seen that propellers of small diameter have in each case 

 proved the most economical and effective, both increasing the 

 speed and decreasing coal-consumption." Mr. Isherwood has 

 shown that decreasing the number of blades in a screw causes no 

 falling-off in speed. Mr. Ericsson's theory was directly opposite 

 in the early da) s of screw navigation. It was considered a pecul- 

 iar advantage in the Ericsson screw that it had six blades. Mr. 

 Griffiths has proved that increasing the hub area up to one-fourth 

 the total diameter does not lessen the speed. Speaking of the tip 

 of the blade, Mr. Barnaby says, " The tip of the blade is very 

 little good, only you must have a tip." The exposed area need be 

 only sufficient to absorb the engine's power: more than this is a loss. 

 Not only were the early engineers mistaken in regard to area, 

 they were equally erroneous in the theory of slip. Mr. W. Froude 

 remarks, " that to assert that a screw works with unusually little 

 slip is to give proof that it works with a large waste of power." 

 He remarks further, " Experiments which have been in progress 

 since this paper has been in type show conclusively that the de- 

 crease of efficiency consequent on increasing slip, with screws of 

 ordinary proportion, is scarcely perceptible." 



