HIPPOPATHOLOGY. 



HOLCUS. 



attention to which points will well repay the 

 parish for the care bestowed upon them, 

 There is a paper, by Mr. Whyte, upon a ma- 

 chine for scraping and cleansing highways 

 (Trans. High. iS'or., vol. iv. p. 349), and on 

 roads, and the excessive weights carried on 

 them in narrow-wheeled wagons, by Mr. 

 Whetly (Com. to Board of Agr. y vol. vi. p. 182); 

 and there is a work on road-making by Sir C. 

 M'Adam, which every road-surveyor should 

 possess. Sir Henry Parnell has also publish- 

 ed a valuable treatise on road-making. Of the 

 materials best adapted to road-making, Mr. 

 Peninld remarks, "The trappean and basaltic 

 recks are those best suited for the construction 

 of roads. No material has ever been used su- 

 perior to the tough basalts, which are brought 

 as ballast in ships from China and Bombay, 

 and which have been partially used in the 

 macadamised streets of London. Limestones, 

 in many respects, afford an excellent material. 

 The more unyielding the material, the smaller 

 is the size to which it ought to be broken. 

 Limestones have in general a peculiar qua- 

 lity of making smooth roads, even if not broken 

 to a small size. Pit gravel, especially that be- 

 longing to the new red sandstone formation, is 

 in general not to be depended upon, as con- 

 taining stones of different sorts, and conse- 

 quently of different degrees of strength. It is 

 one of the greatest mistakes in road-making to 

 lay on thick coats of materials. If there be 

 substance enough already in the road, and 

 which, indeed, should always be carefully kept 

 up, it will never be right to put on more than 

 a stone's thickness at a time." 



HIPPOPATHOLOGY. The science of vete- 

 rinary medicine which comprehends the dis- 

 eases of the horse. Among the writers on this 

 subject, within the last century, may be enume- 

 rated Gibson, Clater, Elaine, Lowson, White, 

 Rydge, Coleman, Dick, Sewell, Percivall, 

 White, Rydge, Stewart, Youatt, and many 

 others ; and although a few of their works may 

 now be obsolete, the greater portion, particu- 

 larly the valuable work of Mr. Youatt contain 

 a vast fund of practical and useful information. 



HOAR FROST. To the authorities quoted 

 in the article FROST, I would add that of the 

 Rev. J. Farquharson. He draws from his ob- 

 servations the conclusions that these frosts 

 occur when the thermometer is at ten feet from 

 the ground, of varying degrees of temperature, 

 sometimes as high as 41; 2dly, that they take 

 place at the time of a high daily mean tem- 

 perature only during a calm ; 3dly, that the air 

 is always, or nearly all of it, unclouded; 4thly, 

 that they most frequently lake place when the 

 mercury of the barometer is high and rising, 

 and when the hygrometer for the season indi- 

 cates comparative dryness. 5thly. In general, 

 low and flat lands in the bottoms of valleys, 

 and grounds that are in land-locked hollows, 

 suffer from these frosts, while all sloping lands 

 and open uplands escape injury. This he ac- 

 counts for by supposing that on sloping 

 grounds there are always currents of air which 

 mix the upper and warmer strata of air with 

 that which rests immediately on the ground, 

 and which it would seem, from some experi- 

 ments of Dr. Wells, is no 4 ; unfrequently much 

 626 



colder than that only four feet from the sur- 

 face. He found, on the 19th of August, 1813 

 (Trans. High. Soc. ix. 250) : 



The slightest protection, even that of a bush, 

 thin sprinkling of straw or litter, is suffi- 

 cient to prevent the deposition of frost, because 

 it is only necessary to prevent radiation. 



HOEING BY HAND. The hand hoe is an 

 instrument too well known to need any de- 

 scription. The operation of hoeing is benefi- 

 cial, not only as being destructive of weeds, 

 but as loosening the surface of the soil, and 

 rendering it more permeable to the gases and 

 aqueous vapour of the atmosphere. Hoeing, 

 therefore, not only protects the farmer's crops 

 from being weakened by weeds, but it renders 

 the soil itself more fertile, as more capable of 

 supplying the plants with their food. Jethro 

 Tull was the first who warmly and ably incul- 

 cated the advantages of hoeing cultivated soils. 

 He correctly enough told the farmers of his 

 time, that as fine hoed ground is not so long 

 soaked by rain, so the dews never suffer it to 

 become perfectly dry. This appears by the 

 plants which flourish in this, whilst those in 

 the hard ground are starved. In the driest 

 weather good hoeing procures moisture to the 

 roots of plants, though the ignorant and incu- 

 rious fancy it lets in the drought. 



HOG CHOLERA. See SWINE. 



HOGWEED (Heracleurn spkondyliuni). The 

 weed known by this name in Pennsylvania 

 and other Middle States, is also called Ragweed 

 and Bitter-weed, the jimbrosia Elatior or Taller 

 Ambrosia of botanical writers. This apparently 

 very worthless weed is common in pastures 

 and cultivated fields, always following the 

 wheat crop immediately after harvest, as 

 though a parasite of this species of grain. If 

 the land be good, the plant seems to give place, 

 the following season, to the crop of clover or 

 timothy. " I have," says Dr. Darlington " been 

 puzzled to determine this species satisfactorily. 

 It is evidently, I think, the Jlmbrosia Elatior of 

 Bigelow, and some others, and as clearly the 

 . artemisifolia of Barton, &c. ; whilst, at the 

 same time, it agrees pretty well with Elliott's 

 A. paniculata. Are they all distinct species? 

 Five or six additional species are enumerated 

 in the United States." (Flor. Cestrica.} 



This plant comes into flower about the mid- 

 dle of May ; its nutritive powers appear to be 

 considerable when compared to those of lucern 

 and some other plants. Sinclair found that 64 

 drs. of the herbage afforded of nutritive matter 

 90 grs., lucern an equal proportion, the same 

 weight of burnet and of Bunias orientalis 100 

 grs. each, of the broad-leaved cultivated clover 

 80 grains. See COW-PARSNIP. (Hort. Gram, 

 Wob.p. 411.) 



HOLCUS. The soft-grass. A genus of 

 grasses of which Smith, in his Eng. Flor. (voL 

 i. p. 107), describes three species, but whicl^ 



