733 



HORSE-POWER. 



HORSE-RADISH. 



734 



made a few years ago for the use of semi-opaque hands and figures 

 on a transparent dial ; with gas lights in a black-cloth lined chamber 

 behind the dial, and reflectors to throw the light on all the sur- 

 rounding objects except the black cloth. General Perronet Thompson 

 has suggested a night clock, with twelve holes cut in a disc for the 

 twelve hours, and a radial slit near the centre to represent a hand ; 

 the disc is to revolve, and gas-lights to be placed behind it. In a fine 

 new turret- clock set up in the Exchange at Leicester, in 1859, the 

 lighting at night is effected by placing two large lenses before the gas- 

 burners, connected by a pierced tube of jets ; so as to light one burner 

 from the other, if either should go out during the day-time, when the 

 gas is turned very low. The illumination is evenly diffused over the 

 dial without glare, and without the position of the burners being 

 distinguishable. 



Clock and Watch Trade. We will conclude with a few observations 

 on the manufacture of clocks and watches, regarded in its commercial 

 and industrial features. 



So far as concerns our own country, the manufacture is chiefly con- 

 ducted in and near London, Coventry, and Prescot. In London, the 

 district of Clerkenwell ia the head-quarters of the trade. The movements 

 of watches are made almost wholly at Prescot and^other places in Lan- 

 cashire ; the London workmen only make the other parts, and put the 

 whole together. A Clerkeuwell watch-manufacturer is one who buys 

 movements from Lancashire, employs smaller tradesmen to fabricate 

 the other parts, and brings the watches into a finished state. These 

 tradesmen are not mere workmen ; they are small master tradesmen. 

 One supplies the motion- work, another the spring, another the escape- 

 ment, and others the case, dial, glass, &c. These secondary masters 

 subdivide the work to a degree almost incredible. Every kind of escape- 

 ment has many different workmen specially employed upon it ; and so 

 has every kind of motion work, hands, dials, &c. ; insomuch that an 

 ordinary London watch passes through considerably more than a hun- 

 dred bands, even after the movement has been brought from Lancashire. 

 Nearly all the workmen thus employed labour at their own houses : 

 the work being quite of a handicraft character, in which very little 

 machinery is employed. The men acquire considerable skill, each in 

 his particular craft ; but it is a system unfavourable for enterprising 

 inventions and cheapening processes, seeing that each man's tact and 

 experience are confined to one very limited range of work. Aa a 

 movement in the right direction, a Horological Institute was founded 

 in Clerkeuwell in 1858 "to develope and improve everything relating 

 to the art, by means of a library of books, a reading-room, a museum 

 of took and machines or models, the reading of lectures and essays, 

 and the publication of a Journal." The principal makers of church and 

 turret clocks live in London, and manufacture nearly the whole of the 

 machinery on their premises. Prescot exports watch movements to 

 America, as well as supplying the home trade ; more machinery is 

 employed in this trade, and to this fact perhaps may in part be 

 attributed the settlement of it iu a county celebrated for its delicate 

 machinery. 



Switzerland is celebrated for its watch-making. The women and 

 children in Neufchatel, and some other cantons, learn certain parts <>f 

 the trade, and find employment in this way, either all through the 

 year, or in the winter, when little out-door work can be done. There 

 is a minute delicacy in Swiss watches which those of England seldom 

 exhibit ; and the selling price is such as no English maker can com- 

 pete with. On the other hand, the bat English watches are not 

 equalled for strength and accuracy by any others in the world. A 

 London manufacturer, Mr. Bennett, has within the last few years 

 endeavoured, by means of letters, pamphlets, and lectures, to foster 

 the introduction pf the Swiss system into England, as a means of 

 increasing the range of employment for women, lowering the prices of 

 watches, and increasing the sale. In the meanwhile, machinery is 

 gradually being brought into the trade in Switzerland and the adjacent 

 part of France. Brukker's small brass clocks, saleable in London retail 

 at only five shillings each, would be a commercial impossibility without 

 the aid of machinery. At Besancon, machine-made watches are now 

 produced in large number* ; the product in 1848 was about 28,000 ; 

 and in 1856 it reached 160,000, worth about 320,0ot>/. 



America has organised a very large system of clock manufactmv 

 quite on Die factory system chiefly in Connecticut. There is one 

 company which employs 250 hands in a compact factory ; many of the 

 operatives are boys and girls ; and the product is 600 clocks per day. 

 Much wood-work is employed in the cheaper American clocks ; but 

 machine-stamped brass clocks are also manufactured very largely. I)r. 

 McOowan, United States consul at Ningpo, wrote home to his country- 

 men in 1853, giving some curious details concerning the clock-trade 

 in China : and offering hints whereby America might successfully open 

 a market in that quarter. 



HOUSE POWER. A term used in mechanical engineering to ex- 

 press the unity of comparison of the power of steam, or water power, 

 machines, whioh is based upon the assumption that a horse is able on 

 the average to perform a certain definite quantity of work within a 

 given time. Constructors of engines differ in their estimates of the 

 value of an average horse power, some reckoning it to be equal to 

 27,500; some to 2,000 ; and others to 33,000 Ibs. raised one foot high 

 per minute. The latter estimate was the one adopted by Watt ; and 

 it is also the one moat generally followed both by English and foreign 



constructors. On this basis a horse power is said to represent a load, 

 in pounds, raised one foot in vertical height, of 550 Ibs. per second ; 

 33,000 Ibs. per minute ; or 1,980,000 Ibs. per hour ; or the effort which 

 7 men working for a short time could exert. 



The formula usually adopted in calculating the horse power of low 

 pressure steam engines is as follows : Calling the effective pressure of 

 the steam upon the piston (beyond the power required to overcome the 

 friction, and the incidental services the engine is called upon to perform, 

 such as the. movement of the feed-pumps, the air-pumps, &c.) calling 

 this effective pressure, supposed for instance to be 7 Ibs. per square 

 inch, A ; the diameter of the piston in inches, D ; and the velocity of the 



piston in feet, per minute, v ; we have the formula X=A* * \ or, in 



00,000 



round munbers = D ' v . In condensing and expansion engines this 



6000 



formula ceases to apply; for the point in the stroke at which the 

 steam is cut off materially affects the effective pressure ; and it is by 

 no means rare to find at the present day that steam-engines will exert 

 a force actually three times as great as the theoretical force indicated 

 by calculation. As the proportions of the various parts of engines and 

 boilers are calculated with reference to the horse power of the engines, 

 this uncertainty in the mode of ascertaining the unity of work is 

 unfortunate, and numerous remedies have been suggested ; such, for 

 instance, as the calculation of the force by means of the weight of 

 steam produced. No confidence can, however, be placed in them, and 

 the old formula is still generally followed. 



Two very rude empirical formulae are adopted by some practical 

 engineers for calculating the horse power of an engine, which may 

 sometimes be of convenient application, as furnishing an approximate 

 means of estimating the value, without, however, attaching any precise 

 importance to the indications so given. They are, calling the diameter 

 in inches, a ; the number of strokes, b ; the length of the stroke in 



English feet,; then HP =^^- S ; or, HP =^^- 



The horse power of a water-fall is really indicated by multiplying 

 the cubic quantity of water falling over the shuttle by the height of 

 the fall and by 62'5 the weight of a foot cube of water being 62 5 Ibs. 

 In the best descriptions of water-wheels, however, a very large portion 

 of the real power is lost by the friction of the machinery, and by the 

 passage of a certain portion of the water without its striking the 

 wheel; and in the more unfavourable varieties the loss is so great as 

 to materially modify the calculated results. Thus Mr. G. Rennie 

 calculates that the effective results as compared to the theoretical ones 

 are, for overshot wheels as 27 or 30 to 100 ; for breast wheels as 45 

 or 50 to 100 ; and for undershot wheels as 60 or 80 to 100. Calling 

 then the quantity of water falling, Q ; the height of fall, H ; and -the 

 co-efficient of the real effective power, expressed decimally, c ; we have 



the formula for a water-wheel HP = QH * - c. 



38,000 



As the usual application of the power of a horse is for the purpose 

 of drawing a load on roads , it may be as well to state, that the useful 

 result of such application must evidently depend on the state of the 

 surface of the roads themselves. This branch of applied science has 

 been studied by Gerstner, Parnell, Gordon, &c. ; and the results of 

 their investigations are expressed in the following empirical formulae. 

 Calling the power exerted, estimated in pounds, p ; the weight of the 

 waggon, w ; the load, w ; the co-efficient for the surface under con- 

 and the velocity in feet per second, v ; we have 



On an inclined road, this formula becomes 



sideration, c ; 



'=< 



* 



40 



>' 



in which k is the vertical 



. 



93 40 I 1 



rise, and I the horizontal length of the incline. The value of c is usually 

 given as = 2 on a paved road ; = 5 on a well made broken stone road in 

 a good state ; = 10 on a similar road when wet and muddy ; =13 on 

 a dry gravel or broken flint road ; and as = 32 on a wet and muddy 

 gravel or broken flint road. Coulomb, and the eftrlier writers on 

 dynamics, considered that the ordinary power of a horse, at a dead 

 pull, was equivalent to 420 Ibs. ; and that he was able to exercise the 

 above force most advantageously, when walking at the rate of 3 feet 

 per second. Smeaton gives the useful effect of a horse walking at that 

 velocity as being equivalent to 189 Ibs. ; this velocity is,nearly at the 

 rate of 2 miles per hour ; but when the velocity becomes 3 miles pel- 

 hour, the useful effect falls to 80 Ibs. Telford gives 200 Ibs. as the 

 actual work of a horse raising a weight over a pulley out of a well, 

 for eight hours in a day, at the rate of 2J miles per hour ; he also says 

 that in a cart, a horse will draw more than 2000 Ibs. For more 

 extended statements on this subject, see the article ANIMAL STKKNOTII. 

 A great deal of curious information may be likewise obtained upon 

 the subject of horse power as usually exerted, in Gordon's ' Treatise 

 on Locomotion,' 1834. Borgni's ' Traitd complet de Mccanique,' 1818, 

 contains, however, the most complete digest of the experiments on 

 the power of men and of animals. 



HORSE-RADISH. Medical Pmptrtietof. Horse-radish is a crucife- 

 rous perennial herbaceous plant, growing in Alpine meadows, and along 

 the banks of rivers, as well as oil the sea-coast in the south and south- 



