M 



WHEEL. 



WHEEL. 



healthy wed. Another disease of the seed IB called ear-cockles, and 

 u eaowd >>y extremely minute insects like eels, which fill the skin of 

 the seed*, iiwtead of flour. This iu*t-t, which is called IV.r.'o //-'.,.. 

 u deecribed by Mr. Bauer in the ' Philosophical Transactions ' for 1823. 

 This disvttse u not to common aa the amut aud the pepper-brand. It 

 U probable, according to Mr. Henalow, that the animalcula may be 

 killed by exposing the grain to a certain heat, no aa not to destroy iU 

 power of vegetation, but sufficient to kill the vibrio. The wheat- 

 midge (L'ttidomyia tntiri) is another external enemy, which does more 

 harm to the crop than is generally known. It deposits ito eggs at the 

 root of the germ in the ear, and prevent* the filling of the grain, the 

 maggot living on thr nutritive juices which should produce the farina. 

 The Hessian fly, which caused such depredations in America and 

 Canada at one time, is a different species of the same fly. This deposit* 

 Ha eggs in the straw near the root, and thus destroys the whole plant. 

 We must refer the reader for further particulars to the p.i[>er above 



. 



Great attention hog been lately paid to the introduction of the best 

 and most prolific varieties of wheat, and by merely observing what ears 

 appear touch superior to others in a field of ripe wheat, and collecting 

 these to be sown separately in a garden or portion of a ticM. the 

 variety, which may have been produced by some fortuitous impregna- 

 tion, or Home peculiarity in the spot where it grew, u perpetuated. By 

 carefully selecting the seed which is best adapted to the soil, by a more 

 careful and garden-like cultivation, and by adding those manures 

 which are found most adapted to favour its perfect vegetation, crops 

 of wheat have been raised, which, at one time, would have been thought 

 marvellous ; and the average produce of this important grain has been 

 increased on all soils. 



WHEEL. A mechanical contrivance, by means of which the inter- 

 mittent and limited action of the lever is extended to any distance, 

 and made to act continuously and uniformly. The direction and the 

 velocity of movement of a machine are commonly regulated by the 

 disposition and character of the wheclwork which enters into its 

 composition ; but tlie principle upon which all wheels really act, con- 

 sists in the application, in a continuous manner, and in a circular 

 direction, of the power obtained by leverage. 



Wheels are either of the kind known as carriage wheels, or j. 

 wheels, or teethed wheels'; including under the second division band 

 wheels, and under the third the various kinds of cog, trundle, pur, 

 cram, and berilled wheels. In a system of wheelwork the wheels 

 may be either multiplying or diminufiiny, according to their relative 

 sizes; they may either perform complete revolutions, or, as in the 

 case of balance wheels, only revolve over small arcs ; they may 

 revolve either horizontally or vertically ; they may be used to produce 

 motion or to communicate it ; or, finally, they may be used for the 

 purpose of regulating the velocity of the machinery to which they are 

 annexed, as in the case of Ay wheels. Water-wheels constitute a sepa- 

 rate class of machinery, known under the same generic name of wheels, 

 in which the power is produced by the direct action upon the wheel 

 itself. [WATER- WHEELS.] In ordinary wheels the power is applied 

 originally to the shaft bearing them, by the intervention of cranks, 

 handles, winches, or levers. 



In carriage wheels the object sought to be attained is to convert a 

 sliding friction into a rolling one, in order to facilitate the horizontal 

 movement of heavy loads. The efficiency of a carriage wheel, there- 

 fore, consists in the length of the lever it offers (or, in other words, 

 upon its diameter) ; upon the direction in which the power is applied 

 to it ; and upon the small extent of surface producing friction ; always 

 provided that the surface should be sufficient to prevent the load from 

 forcing the wheels into the materials over which they run. It is for 

 the avowed object of insuring the application of the power exercised 

 by a hone, in drawing a cart or carriage, abort the horizontal line 

 palming through the centre of the fore wheels, that they are made 

 smaller than the bind wheels ; but, as an abstract proposition, it may 

 be stated that the larger a wheel is, the greater is the useful effect it 

 produces, provided the line of draught pass horizontally through its 

 centre. Another abstract proposition with respect to carriage wheels 

 is, that the narrower their surfaces, the less friction they must de- 

 velope ; but evidently the character of the roadway over which the 

 load travels must re-act upon this condition, for u|n a soft surface a 

 narrow wheel, heavily laden, would compress the road materials, and 

 thus create a continually occurring series of obstacles to its own pro- 

 gress Upon soft roadways, under heavy loads, carriage wheels must 

 therefore be made wide upon the face of the felloes ; for quick traffic, 

 on hard roads, when the carriages do not convey heavy loads, narrow 

 wheels are generally resorted to. 



In the earliest wheeled carriages, the wheels were made of solid 

 planks, and the axle* were fastened to them, so that wheel aud axle 

 turned together; the load in such cases being borne upon collars 

 worked upon the axles. Rude carts of this description have been 

 used in England within a very short period, and they may still be seen 

 upon the provincial roads of such countries as Spain or southern 

 Italy. When the roads are habitually of a superior character, l.-.w- 

 ?er, carriage wheel* are made as lightly as the work they are 

 required to perform will admit of ; and they consist usually of a nan, 

 cr centre bow, into which the ijiotei or radiating arms are fastened at 

 MM end, whilst the spokes at their other ends bear the fclloci ; the 



whole assemblage being bound together by an iron lire, nailed t- the 

 felloes whilst it is hot, in <>nU-r tli.it the shrinkage of the iron in 

 cooling may " force t&e Tarioni joint* h.nne," as workmen say. The 

 nave is usually bored out to receive a />.< of iron (or of gnu n. 

 some cases), in which the collar of the axle is inserted, so that the 

 wheels on the respective sides of the carriage can revolve ii 

 of one another in their horizontal positions, but ore maintained at fixed 

 distances apart horizontally. In wheeled carriages thu bodies are 

 attached to the axles, cither with, or without, the inttrv, n: 

 springs ; in four-wheeled carriages the front pair of wheels is usually 

 made to revolve on a pivot fixed under the fore part of the body. Of 

 course the dimensions of all the details of carriage wheels i 

 upon the weights they are intended to transport, and up"ii tin- velocity 

 at which they are intended to travel ; in railway carriages the naves, 

 spokes, felloes, and tires of the whit-Is arc executed of iron, or of steel ; 

 in common carriages, wood is tin- matt rial principally used. 



The friction wheels of mill-work are introduced for the same purpose 

 that wheels are adapted to ordinary carriages ; that is to say, f< >) the 

 purpOM :ing sliding friction into rolling friction. They are 



used to facilitate the horizontal or vertical mi i traversing 



beds, of guide rods, &c., and therefore the only conditions tli 

 required to fulfil are, that they should revoh tin ii own 



axles, and present smooth surfaces (able to retain a lubricating thud) 

 to the bodies moving over them, or over which they may 

 Driving baud-wheels, on the contrary, arc fixed on their bearing shafts, 

 and have their surfaces formed in such a manner as to cause the straps, 

 or bands, to adhere to them by their mere friction upon the asperities, 

 and thus to produce motion in the secondary band-wheels of the 

 machinery to which they arc applied, by the rotation of the first 

 wheels. In some cases also, motion is communicated by means of 



wheels whose surfaces are in contact, aud which act upon one another 

 by the mere unevenuess of those surfaces ; if, however, any serious 

 resistance should be encountered, the wheels would be likely to slide 

 over one another, and they are therefore only used in light anil delicate 



machinery. Indeed all descriptions of band-wheels are exposed to the 

 same objection, because they only communicate motion by the friction 

 of the bands upon the respective surfaces, and when the resistance 

 exceeds that friction, the bands must slide over the wheels ; but they 

 present so many facilities for the introduction of *ptcil pulleys, (that is 

 to say, of pulleys by means of which the rate of revolution may be 

 modified at will) that they are constantly resorted to in machinery, 

 especially when it is desirable to avoid making a noise. Band-wheels 

 are commonly arranged so as to present on the same axle, and in 

 immediate proximity to one another, what are called fant and loote 

 pulleys ; the fast pulleys] being fixed upon the axle, so that the two 

 must turn together, whilst the loose pulley turns freely UJMMI the axle, 

 and does not communicate any motion to the latter. When, therefore, 

 it is desired to put band-wheels with fast and loose pulleys out of gear, 

 all that is required to be done is to pass the band upon the loose 

 pulley, and the communication of the movement immediately 0"" 



Baud-wheels also present great advantages from the ease with which 

 they admit of the change in the direction of the motion. If, for 

 instance, it be desired to reverse the motion, the baud is simply crossed, 



