746 



SCIENCE. 



IVoL. II., No. A1. 



surfaces for which the problem can be solved are di- 

 vided into certain classes. M. Darboux gives the ex- 

 pressions for the co-ordinates of a point in terms of 

 two parameters for the surfaces of the first class. — 

 (Compte.s j-eiidMS, March 19.) T. c. [441 



ENGINBEEING. 

 Theory of the scre-w-propeller. — Mr. J. N. 



Warrington, of the Stevens institute of technology, 

 discusses the theory of the screw-propeller, and the 

 methods of designing it. He first discusses the action 

 of the screw in the water, investigates the conditions 

 of maximum efficiency, and obtains expressions for 

 the efficiency in terms of the angle of the blades, and 

 the ratios of resistance of friction to pressures ex- 

 erted. He finds, as does Fronde, that the angle of 

 maximum efficiency is forty-five degrees. It is found 

 that a small amount of slip does not necessarily give 

 good performance, — a conclusion already proven by 

 experience. It is found that the action of the screw, 

 in its most efiicient operation, does not involve the 

 sternward projection of a solid stream; and hence 

 it follows that all investigations based, as is common, 

 on that assumption, are inaccurate. Yet it is only 

 the water that is thrown aft that gives propelling- 

 power, and the nearer the stream is solid, the better. 

 He obtains the equation of the curve of the devel- 

 oped screw from Thurston, and expressions for the 

 magnitudes of diameter and thrust from Seaton. 

 The second part of the p.aper is devoted to the 

 designing of the screw according to the principles 

 deduced in the first part. The shape of a blade 

 upon which the water shall glide without shock, and 

 from which it shall be thrown aft with a given velocity, 

 acquiring that velocity by a uniform acceleration, is 

 given by its equation as deduced by Warrington. 

 The relation between the pressure and the accelera- 

 tion is ascertained; the slip is assumed, and the total 

 resistance is given ; and the required size of screw is 

 calculated. The magnitude of the losses of energy, 

 and the efficiency, are determined, and the process is 

 applied to the guide-blade propeller as well as to the 

 common screw. Two wheels are drawn,' — the one 

 a U. S. naval-department screw, the other a screw 

 designed on Warrington's plan. — {Juurn. Frankl. 

 inst., Aitg.) R. II. T. [442 



Light prime motors. — President D. Napoli, of 

 La soci(5iiS de navigation a^rienne, in a communica- 

 tion to the Aeronaute, compares the weight of steam- 

 engines and electric motors for use in aeronautics. 

 He finds that the weight of fuel and water demanded 

 by a steam-engine of twenty-horse power for ten 

 hours' work would be not far from 1,600 kilos (;!,527 

 lbs.), while the weight of an electric motor and its 

 supplies would bo about 1,400 kilos (3,087 lbs.); giv- 

 ing a decided advantage to the latter aside from the 

 weight of the engine, which may be anywhere from 

 two hundred and fifty to four hundred per cent 

 greater than the weight of its supplies, according to 

 style, which M. Napoli does not prescribe. — {Chron. 

 ind.,Jnne. ) R. ii. t. [443 



Resistance of rail'way-trains. — Profe.>-sor Franck 

 has written a memoir on the resistance of trains, 



studying the earlier experiments of Vuillerain, Gueb- 

 hard and Dieudonne, and of Rockl. lie obtains the 

 formula for resistance, 



, IFv- 

 w = m -I — — , 



in which i« is the resistance in kilos per ton, Q is 

 the weight in tons, m, I, and F are the coefficients, 



as follows: — 



For passenger-engines . . m = 0.0032 

 " freight-engines. . . m = 0.0038 to 0.00:!'.> 



" the cars m = 0.0025 



" all cases I = 0.1225 



" passenger-engines . . F = 1 

 " freight-engines . . F = 8 

 " passenger & box cars, F = 0..") 

 " unloaded flat cars . . J^ = 0.4 

 " loaded flat cars . . . F = 1.0 

 The author of the paper considers that this for- 

 • mula, used with this assortment of constants, will 

 allow of very exact calculation of the resistance of 

 trains. — {Mem. soc. ing. civ., June.) n. H. T. [444 

 Dowson's gas for heating. — In 1SS2 the Messrs. 

 Crossley put in a Dowsou plant for making his gas. 

 The trial of the system gave the following results: 

 when the gas was made from Trimsaran anthracite, 

 a gas-engine consumed 1..5 pounds (O.GS kilogram) 

 per hour per horse-power; when using Garnant an- 

 thracite, the consumption was 1.4 pounds {0.li4 kilo- 

 gram). These results were so satisfactory that the 

 Messrs. Crossley have adopted the gas-engine through- 

 out their works, and are using some 200-horse power. 

 The engine above referred to was of about .30-horse 

 power. It is found that a larger engine, 40-horse 

 power, uses but 1.2 pounds (0..54 kilogram). The 

 l>rocess consists in passing a current of steam and air 

 through a mass of red-hot carbonaceous materials. 

 Coal-gas has nearly four times the heating-power of 

 this gas, but the cost of the Dowson gas is so much 

 less that it compensates this great difference. It is, 

 however, intended to compete with the gas produced 

 from coal-oils. The author of the paper calculates 

 that the costs of operating a steam-engine, and of 

 working a gas-engine driven by his gas, are as three 

 to two, the engines being of 100-horse power each. — 

 (Proc. Inst. cii). enij., 1883.) R. ii. t. [445 



AGEICULT0RE. 

 Reversion of superphosphates in the soil. — 



Farsky shows, that, when a small quantity of water 

 acts upon a superphosphate, the monocalcic xjhos- 

 phate which it contains is decomposed into dicalcic 

 phosphate and free phosphoric acid. The same pro- 

 cess seems to take place when a superphosphate is 

 mixed with the soil. Subsequently the free acid ap- 

 pears to act upon the calcium, iron, and aluminum 

 salts of the soil, forming dicalcic phosphate and sol- 

 uble acid phosphates of iron and aluminum. The 

 latter are not stable, and soon pass into insoluble 

 combinations (compare Science, i. 825). — {liieder- 

 mamVs centr.-blatt., xii. 450.) n. P. A. [446 



Fineness of superphosphates. — Farsky, both 

 in pot-experiments with buckwheat, and in field-ex- 

 peiiments with several other cropSj found that coarse 



