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THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[December, 



as respects the application to separate and revolving lamps, the experiment 

 has been made under the direction of the Trinity House, on a face of six 

 lamps, being a full-sized copy of the Tynemouth revolving light, and, so far 

 to the satisfaction of the Dep ity Master and Brethren, that the plan is to 

 be applied immediately to two light-houses which suffer most from conden- 

 sation on the glass; he believes it will be with full success. 



A Lock-meter. 



11 A model and drawing of a Lock-meter, uied in Lombardy for measuring 

 Water for Irrigation," were presented by Benedetto Albano, M. Inst. C. E. 



The author stated that the necessity for regulating the supply of water for 

 irrigation, had induced the adoption in Lombardy of a meter, with an aper- 

 ture of given dimensions, as a standard for the emission of water to the irri- 

 gating channels — this was terruri the " Bocche Magistrate." This standard 

 was called " oncia d'acqua magistrate," by which was understood, a quantity 

 of water flowing through a given aperture, under an unvarying pressure, 

 permitting only the passage of a certain quantity per minute. This " oncia 

 d'acqua " has now been ascertained by Krenzlin (Inspector General of Canals, 

 Milan) to be equal to 2'12 cubic metres per minute, and is now the received 

 authority; and the system is adopted through the Lombardian and Venetian 

 Kingdoms, and other provinces of Italy. This quantity is supposing the 



flow to be through an aperture 3 oncie 3 wide by 4 high, and with a head of 

 water of 2 oncie. An oncia is equal to 1*95 inches. 



The structure consists of an aperture A, where the water is measured, 

 nearly 8 inches high, 16 inches broad, and 6 inches long, leading to which 

 is the channel C, 20 feet long, which has a floor inclined to the supplying 

 stream B, at an angle of 1 in 15 ; this channel is covered by a horizontal 

 close boarding or ceiling D, by which the undulatory motion of the water is 

 checked and any air is prevented from getting into the channel, while the 

 height of the head is restricted to 4 inches above the aperture A. At the 

 end is a sluice-gate H, of the same width as the aperture A, to be raised by 

 a rack I ; on the gate is a block K, to prevent its being raised too high, and 

 a bolt and lock secure it. The discharge channel F, is about 18 feet long, is 

 inclined 1 in 108, and widens about 4 inches at each side, diverging out- 

 wards nearly 6 inches in the entire length. Care must be taken that the 

 water in the channel at G, is always kept below the bed of the channel F. 

 The sluice-gate being opened sufficiently to fill the covered channel up to 

 the ceiling, the quantity of water flowing through the aperture is accurately 

 measured. Just behind the sluice there is a small opening to see when the 

 water has reached the proper level. The aperture A, to this metre will allow 

 a discharge of 1272 cubie metres, or 449 cubic feet, English measurement, 

 per minute; beyond these proportions the aperture is not allowed to be in- 

 creased, as there would be a sensible error in the quantity on account of the 

 vena contracta. 



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" On the Pressure and Density of Steam, with a proposed new formula 

 for the relation between then ; applicable particularly to Engines working 

 with high-pressure Steam expansively." By William Pole, Assoc. Inst. C. E. 



The relations between the elasticity, temperature, and density of steam 

 have long been interesting and important subjects of philosophical research. 

 The connexion of the two former, namely, pressure and temperature, with 

 each other, has excited the greatest attention, numerous experiments having 

 been undertaken to ascertain the values of them at all points of the scale, 

 and many formulae proposed by English and foreign mathematicians, to ex- 

 press approximately the relation between them. 3 



The pressure and temperature being known, the density, or what answers 

 the same purpose, the relative volume, compared with the water which has 

 produced it, may be deduced by a combination of the laws of Boyle • and 

 Gay Lussac; 5 and may be expressed algebraically in terms of the pressure 

 and temperature combined ; whence, by eliminating the latter, by means of 



* Upwards of twenty different formula? of this nature are given in the 

 Encyclopedia Britannica, 7th edition, art. "Steam," where their respective 

 merits and correspondence with the results of experiment, are amply inves- 

 tigated. 



* That "if the temperature remain constant, the density varies directly 

 as the pressure." 



6 That " if the pressure remain constant, and the temperature change, the 

 volume receives a certain definite amount of augmentation, tor each degree 

 of temperature added, or vice versd." This augmentation is equal "00208 ot 

 the volume at freezing point, for each degree of Fahrenheit, or '00375 for 

 each degree Centigrade. 



the before-mentioned formulae, expressions can be arrived at which will con- 

 nect at ouce the volume with the pressure. 



But there are several difficulties in the way of this process, the equations 

 which mav be thus obtained being too complicated for practical use ; and 

 therefore, since it is important in calculations connected with steam and the 

 steam-engine, to find a tolerably accurate, and at the same time, simple rule 

 which shall give the pressure and volume directly in terms of each other, 

 the empirical method has been resorted to. 



The paper enumerates three formula; given for this purpose by M. Navier 

 and M. de Pambour, explaining the peculiar cases to which they are appli- 

 cable, and those in which they fail ; and the author then proposes a fourth 

 expression, which is intended to meet a case not provided for by either of 

 the others, namely, for " condensing engines working with high-pressure 

 steatn expansively ;" such as the Cornish, and Woolf's double cylinder engine . 

 The equation is — 



24250 

 V-65' 



or reciprocally, V 



24250 

 "~P~ 



+ 65. 



P being the total pressure of the steam in lb. per square inch, and V its re- 

 lative volume, compared with that of its constituent water. 



These formula; may be adopted without considerable error, throughout the 

 range generally required in such engines, viz., from about 5 lb. to 65 lb. per 

 square inch. 



Two tables are then given showing the pressures and volumes as calcu 



