DUCK'S FOOT. 



DUCK'S FOOT (PodophyJlum ; a bridged 

 from inKijioilo/ihijllinn, a wont signifying a duck's 

 foot, as the leaves bear some resemblance to 

 it). This plant requires a moist, shady situa- 

 tion, and to be grown in peat soil ; increased 

 by division at tin- root. (Ptucton's Hot. Dirt.} 



DUCKWEED (Lemna). A genus of minute, 

 herbaceous, floating plants, consisting of four 

 species, all of which are natives of England, 

 :nw abundantly in ponds, ditches, and 

 stagnant waters. They are in flower from 

 June to August. Duckweed is a small green 

 herb, consisting of little roundish leaf-like 

 disks. It is not, perhaps, generally known that 

 duckweed, if allowed to spread itself over 

 ponds and stews, in which fish are preserved, 

 will ultimately destroy them, by its forming a 

 compact mat upon the surface, thereby prevent- 

 ing the fish, when they rise to the surface of 

 the water for air, from breathing. It should 

 on this account be abstracted diligently with a 

 rake, or some such implement, and kept under 

 before it attains an ascendency, which it will 

 do in a very short time if not seasonably with- 

 drawn. The quantities of fish that perish 

 under the influence of this weed are incal- 

 culable. Ducks feed upon the " lemna" with 

 surprising avidity, and thence it derives its 

 name (duck's meat or duckweed). Ducks, by 

 dabbling and grovelling in foul pools, where it 

 predominates, and its adhering to their feathers, 

 are in the habit of introducing it into other 

 waters, where it never appeared before. (Eng. 

 Flora, vol. i. p. 31 ; Witticti* Dom. Ency.) 



DUN (Sax. tiun). A colour partaking of 

 brown and black, frequent in horses. 



DUNES (Ang.-Sax. low hills). Hills of 

 movable sand, which are met with along the 

 sea coast in various parts of Great Britain, 

 Ireland, and the Continent. (Brandc's Dut. of 

 Science.) 



DUNG and DUNGHILL. See FARM-YARD 

 DUNG and COMPOST. 



DURHAM CATTLE. See CATTLE. 



DUST BRAND. One of the local names 

 for the smut in wheat. 



DUTCH ASHES. See ASHES. 



DUTCH ELM (Ulmus subcrosa). See ELM. 



DWARF BAY. See MEZEREO*. 



DWARF ROSE BAY. See MOUNTAIX 

 LAUREL. 



DWARF BERRIES. See NIGHTSHADE. 



DWARF OAK. A shrub, sometimes em- 

 ployed for making live fences. It grows very 

 fast, and becomes thick by cutting very ra- 

 pidly. 



DYKE (Sax. t>ic; Erse, dylc). A sort of wall 

 or mound formed of earth or turfs. In Scot- 

 land it is applied to any wall round a field. 

 See DITCH. 



DYNAMOMETER (Gr. Jwtptf, power, and 

 ftsTgif, measure). An instrument for measur- 

 ing power of any kind, as the strength of men 

 and animals, the force of machinery, &c. 

 Some interesting results relating to the average 

 strength of men at different ages, and of dif- 

 ferent weights and sizes, have been produced 

 by M. Quetelet of Brussels, from numerous 

 experiments with Regnier's dynamometer, one 

 of the most convenient that is made. 



It consists of two flat plates of steel of a 

 426 



EAR. 



curved form, increasing in thickness towards 

 the ends, which unite into solid cylindrical 

 loops ; the curved sides of the plates being 

 placed opposite to each other, and the whole 

 forming an entire elliptic spring. On the ap- 

 plication of this instrument as a link in the 

 line of draught, the oval becomes lengthened 

 in proportion to the degree of force acting on 

 the loops in opposite directions, and the curved 

 sides approach more nearly towards each 

 other accordingly. The degree of approxima- 

 tion in the plates is shown on the scale, in 

 divisions corresponding to half and whole hun- 

 dred weights, by means of a cross rod secured 

 to one plate acting on a crank attached to the 

 opposite one, thus communicating its effect to 

 the lever index, which, moving over the divi- 

 sions of the scale, marks the varying degree 

 of force exerted each moment by the draught 

 to which the instrument is subjected. 



Messrs. Cottam and Hallen, engineers and 

 agricultural implement makers, of Winsley 

 street, Oxford street, London, have recently 

 patented an improved dynamometer, contrived 

 with the intention of obviating the continual 

 vibration of the indicator of the dynamometer 

 formerly in use, which was caused (with refer- 

 ence to the plough) by the obstructions met 

 with in the soil through which it was passing. 

 These vibrations were so incessant, that the 

 indicator could scarcely be discerned during 

 the experiment. The improvement consists in 

 the attachment of a small brass pump filled 

 with oil, the piston of which has one or two 

 small apertures. There being no outlet from 

 the pump, it is evident that when any shock 

 occurs, caused by a stone, root, &c., the oil 

 having to pass from one side of the piston to 

 the other, the suddenness is greatly diminished 

 by the resistance, producing a corresponding 

 effect upon the pointer, which, as these shocks 

 are rapid, vibrates nearer the actual draught 

 of the machine ; which is the object in view, 

 and not the measurement of any impediment, 

 but a mean result of the whole. Mr. Pusey, in 

 his "Experimental Inquiry on Draught in 

 Ploughing" (Journ. Ray. Eng. Jlgr. Soc. vol. i. p. 

 219), speaks very favourably of this draught- 

 guage, and remarks (Ibid. p. 222) : " Such is 

 the goodness of Mr. Cottam's new draught- 

 guage, that we scarcely ever, I believe, differed 

 by more than a quarter of a hundred weight, 

 and often agreed to an eighth, or one stone." 



DYSENTERY (Fr. dysenterie). See SHKEP, 

 DISEASES OF. 



E. 



EAR (Sax. eajie; Lat. auris). The organ of 

 hearing in animals. In a horse, the ears should 

 be small, narrow, straight, and the substance 

 of them thin and delicate. They should be 

 placed on the very top of the head; and their 

 points, when stiled or pricked up, should be 

 nearer together than their roots. When a 

 horse carries his ears pointed forwards, he is 

 said to have a bold or brisk ear. In travelling, 

 it is considered an advantage when the horse 

 keeps them firm. The exterior ears of the 

 horse are merely organs for collecting bound 



