Online Encyclopedia
Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.
HARROW
Online EncyclopediaEncyclopedia Home :: HAN-HEG
del.icio.us it!
|
HARROW ,1 an agricultural See also:implement used for (I) levelling ridges See also:left by the plough and preparing a smooth See also:surface for the reception of seeds; (2) covering in seeds after See also:sowing; (3) tearing up and gathering weeds; (4) disintegrating and levelling the See also:soil of meadows and pastures; (5) forming a surface tilth by pulverizing the See also:top soil and so .conserving moisture. The harrow rivals the plough in antiquity. In its simplest See also:form it consists of the boughs of trees interlaced into a wooden See also:frame, and this form survives in the " See also:bush-harrow." Another old type, found in the See also:middle ages and still in use, consists of a wooden framework in which See also:iron pegs or " tines " are set. This is now generally superseded by the " zig-zag " harrow patented by See also:Armstrong in 1839, built of iron bars in which the tines are so arranged that each follows its own track and has a See also:separate See also:line of See also:action. This harrow is usually made in two or three sections which See also:fold over one another and are thus easily portable, the arrangement at the same See also:time giving a flexibility on uneven ground. Additional flexibility may be imparted to the implement by jointing the stays of the frame which are in the line of See also:draught. The liability that the tines may snap off is the See also:chief weakness of this type, and improvements have consisted chiefly in alterations in their shape and the method of fixing them to the frame. The other type of harrow most used is the See also:chain harrow, consisting of a number of square-See also:link chains connected by See also:cross links and attached to a draught-See also:bar, the whole being kept See also:expanded by stretchers and trailing weights. It is used for levelling and spreading manure over grass-See also:land, from which it at the same time tears up See also:moss and coarse herbage. Mention may also be made of the See also:drag-harrow, a heavy implement with See also:long tines, approximating closely to the See also:cultivator, and of the See also:Norwegian harrow with its revolving rows of spikes. A few See also:variations and developments of the See also:ordinary harrow require See also:notice. In the adjustable harrow (fig. 2) the See also:teeth are secured to bars pivoted at their ends in the See also:side bars of the frame, and provided with See also:crank arms connected to a See also:common link bar, which may be moved horizontally by means of a See also:lever for the purpose of adjusting 1 In See also:Mid. Eng. harke; the O. Eng. appears to have been kearge; the word is cognate with the Dutch hark, Swed. harke, Ger. Harke, See also:rake, and with Danish See also:hare, and Swed. harf, harrow, but the ultimate origin is unknown; the Fr. herse is a different word, cf. See also:HEARSE. the See also:angle which the teeth make with the ground, and thus convert the See also:machine from a pulverizer to a smoothing harrow. The small figure illustrates a See also:spring connexion between the adjusting lever and its locking bar, which allows the teeth to yield upon striking an obstruction. As the briskness of the operation adds to its effective- ness, the harrow is often made with a seat from which the operator can hasten the team without fatiguing himself. Fig. 3 illustrates a spring-tooth harrow. In this harrow the in-dependent frames are carried upon wheels, and a seat for the operator is mounted upon See also:standards supported by the two frames. The teeth consist of See also:flat See also:steel springs of See also:scroll form, which yield to rigid obstructions and are mounted on See also:rock shafts in the same manner as in the walking harrow before described. The levers enable the operator t o raise the teeth more or less, and thus See also:free them from rubbish and also regulate the See also:depth of,,action. Another variation of the harrow with See also:great pulverizing and loosening capabilities consists of a See also:main frame, having a See also:pole and whipple-trees attached; to this frame are pivoted two supplemental frames, each of which has mounted on it a See also:shaft carrying a See also:series of concavo-See also:convex disks. The supplemental frames may be swung by the adjusting levers to any, angle with relation to the line of draught, and the disks then See also:act like that of the disk plough (see PLOUGH), throwing the soil outward with more or less force, according to the angle at which they are set, and thus thoroughly breaking up and pulverizing the clods. Above the disks is a bar to which are pivoted a series of scrapers, one for each disk, which are held to their See also:work with a yielding action, being thrown out of operation when desired by the levers shown in connexion with the operating bar. Pans on the main frame are used to carry weights to hold the disks down to their work. The cut away disk harrow differs from the ordinary disk harrow in that its disks are notched and so have greater penetrating See also:power. The curved See also:knife-tooth harrow consists of a frame to which a See also:row of curved See also:blades is attached. Other forms of the implement are illustrated and discussed in See also:Farm Machinery and Farm See also:Motors by J. B. See also:Davidson and L. W. See also:Chase (New See also:York, 1908). Additional information and CommentsThere are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML. Site content, images, and layout Copyright © 2006 - Net Industries, worldwide. |
|
|
[back] HARROGATE |
[next] HARROWBY, DUDLEY RYDER, 1ST EARL, OF (1762–1847) |