HOAR-FROST. 



HOE, HORSK-HOI:IM; 



and institutions of the actual generation. Thi- 

 ef universal change and complete refomiation of social 

 habiU and opinion* is indulged in for a few abort years, sometimes 

 mingled with contempt of thane who pertinaciously look Iwhind them, 

 Instead of embracing the offered means of perfectibility and throwing 

 awaj all doubU a* to the future. An in-truer r.e lemon is all lint 

 remains of these brilliant expectation*. We Irani the folly of wrestling 

 with a power which we hare nnt duly estimated, and of opposing to 

 opinions and habits hardened by the growth of centuries, even the 

 noundest conclusions of our philosophy, when unaided by the experience 

 ;..- q 



HOAR-FROST. The circumstances of terrestrial radiation, chiefly, 

 but not exclusively, nocturnal, umler which the aqueous vi\|'iir of the 

 atmosphere becomes condensed upon the bodies in contact with it, 

 hare already been discussed and explained at some length in the article 

 Diw. If the temperature of those bodies be reduced below the 

 freezing point of water, hoar-frost is produced, the most characteristic 

 form of which differs from dew only " by being frozen in the moment 

 of deposition, and therefore accreting in crystalline spicuUe." But it 

 occasionally happens, as also mentioned already, that after the globules 

 of water constituting dew have been deposited, they are frozen, and 

 become another form of hoar-frost. 



In calm weather of the requisite low temperature, without fog, hoar- 

 frost is seen in great perfection, especially in those mornings which 

 are preceded by clear and cold nights, accompanied by a great deposi- 

 tion of moisture, or of what would have been moisture had not the 

 freezing process interfered. It then imparts to tree* and shrill's, and 

 out-door objects in general, a great degree of beauty and richness of 

 effect, fringing the leaves of plants with myriads of spiral*, suspended 

 either parallel to each other, or inclined at various angles, of all lengths, 

 crossing and reoroaring, and forming innumerable' combinations. In 

 some observations by Mr. GUisher, first published in the ' Philosophical 

 Transactions' for 1347, and subsequently in the Report of the Council 

 of the British Meteorological Society for 1854, he describes the manner 

 in which these spiculie were formed on various plants. " The leant of 

 tht laurtl," he found, " were fringed with spikes one-tenth of an inch in 

 length, and inclined to the leaf both upwards and downwards at an 

 angle of 60 ; but none were in the plane of the leaf continued. On 

 the surface of the leaf were spikes down each fibre, one-sixteenth of an 

 inch in length. The leaf itself, in the intermediate spaces, was covered 

 with small white particles. The leare of the print were richly fringed 

 with spikes for a quarter of an inch within the leaf ; the spikes were 

 about a quarter of an inch in length. .... /(room was most richly 

 encrusted with spikes all round ; by far the greater number, and longer 

 than the rest, springing from the sides of each branch. There were 

 comparatively few on the top, and none there were vertical. . . . Gran 

 was very beautiful. The blade I found to be covered with white par- 

 ticles, which increased to spikes, becoming longer and larger the further 

 from the root, terminating at the top in a rich circular cluster of 

 spikes, set at all angles from to 60, and one-tenth of an inch in length. 

 The spikes towards the end of the blade were nearly horizontal, or in 

 the plane of the blade continued. The lower part towards the root 

 was free and untouched by frost." From this latter circumstance, and 

 that previously mentioned of the increase in magnitude of the spikes 

 in proportion to their distance from the root, it may be inferred that 

 the vegetable heat in that region of the plant counteracted the reduc- 

 tion of temperature by radiation, which had occasioned the drj 

 of hoar-frost on the blades. 



Guided as he had been in his experimental researches on terrestrial 

 radiation, and on the deposition of dew, by those previously instituted 

 by Dr. Wells, Mr. Ulaisher made a series of experiments also on the 

 formation of hoar-frost on various substances exposed to the atmos- 

 phere under the requisite conditions. 



Glass, raised one inch high above the ground, was covered with spikes 

 one-sixteenth of an inch in length, and all arranged horizontally at the 

 edges. Olass on grass was free from hoar-frost, doubtless nn account 

 of the greater radiating power of the latter, the atmosphere in contact 

 with the glass remaining at a higher temperature. 



On metals, such as copper, lead, rinc, tin, iron, &c., then.' were 

 neither lamina? nnr spikes of any kind ; but tin, raised one inch high, 

 was a little whitened at the edges. 



Of three forms of carbon, all powerful radiators, on charcoal and 

 graphite there were spikes in rich clusters, each group radiating from 

 the same point, the spiculic being generally inclined at all angles ; and 

 on lamp-black the spikes were very numerous, being about three- 

 eighths of an inch in thickness, and inclined at an angle of about 30*, 

 and at all azimuths, or in every direction with respect to the cardinal 

 points ; each cluster formed a circle, in the centre of which there were 

 no spikes. 



On sand there were spikes one fourth of an inch in length. Chalk 

 Was covered with a mass of spikes of the same length. Whiting, which 

 is chalk prepared by grinding, and suspension in water, and fill-sequent 

 slight consolidation, was covered with rich bunches of spikes three 

 eighths of an inch in length. 



Of cotton wool, every fibre was encrusted with a beautiful fringe of 

 hoar-frost, ami there were also a few spikes of ice. t>>n flax there 

 were no spikes, it being covered with white round particles (globules 

 of dew frown T) with small sparkling flakes of ice. Wood was covered 



with spikes a quarter of an inch in thickness, inclined to the horizon at 

 in angle of 60', and at all azimuths. Sawdust was very beautifully 

 covered with xpicuto fans, formed by several spikes emanating from 

 the same point at all angles greater than SO* with the horizon. These 

 spikes were connected with each other by lateral spikes or bands, the 

 whole forming the appearance of a fan, whose extent was 120*. Paper 

 was covered with small round particles and a few spikes. 



Raw wool was richly clustered on each fibre, so as to be about six 

 times its own site ;' the spikes were three-fourths of an inch in length. 

 and piled one upon another. Raw wool raised was similarly covered 

 to flax, and displayed only a few spikes running in the direction of its 

 fibres. 



Raw silk was covered with spikes one-sixteenth of nn inch in length, 

 two of which emanated from the same point, at right angles to the 

 fibre, and whose angle of separation was SO'. 



The various modes of aggregation of the minute crystals of Ice 

 which constitute hoar-frost, are evidently dependent on differences in 

 the texture, and in the radiating and conducting powers of these 

 materials, and present a field for investigation hitherto little cul- 

 tivated. 



In England generally, as the observations of the late Professor 

 Daniell, confirmed by the researches of Mr. Glaisher, have shown, 

 vegetation is liable to be affected at night, from the influence of 

 radiation, by a temperature below the freezing point of water, every 

 month in the year, even in July and August. This explains the 

 observed fact of the existence of hoar-frost in the early morning, in 

 every season, even in the mildest climates of this country. 



But in the Island of Guernsey, in .the English Channel, where frost 

 in general i* neither frequent nor lasting, hoar-frost, according to 1'r. 

 Samuel Elliot Hoskins, F.R.S., is also of rare occurrence, owing 

 partly to the high night temperature, and partly to the constant 

 presence of a breeze, more or less fresh. Neither is hoar-frost general 

 in the island when it does take place, being confined to elevate < 

 bleak situations, and chiefly limited to the months of Januni;. 

 February. Spring vegetation here therefore is rarely checked by that 

 condition which seriously interferes with early crops, even in the mjld 

 districts of Devonshire and Cornwall, where the husbandman is often 

 driven to the necessity of protecting early vegetable productions by 

 slight layers of straw, in order that they may not be chilled l.y their 

 own radiation and the consequent deposition of hoar-frost upon them ; 

 or to the more troublesome operation of lighting fires to windward 

 during cold clear night*, in order to produce a warm and virtually 

 cloudy local atmosphere, and so to counteract the radiating process 

 and its consequences. 



Ice is also formed on the stems of plants and on certain inorganic 

 bodies, by a process very different from that resulting in the produc- 

 tion of hoar-frost, with which, however, it is popularly confounded. 

 The facts respecting it will be stated in another article. 



[DEW; HAIL; ICE; METEOROIOOV; RADIATIOX OF HEAT; Sxow.] 



HOE, HORSE-HOEING. The hoe is an instrument used in 

 gardens and in the fields for loosening the earth, and destroying the 

 weeds between plants. It has various forms. The most common hoe 

 consists of a blade or flat piece of iron, with an eye in which a handle 

 is inserted at an acute angle with the plane of the blade. This r 

 used by striking the edge of it down into the ground, and the earth is 

 moved by drawing the handle towards the workman. Another hoc has 

 the handle at a very obtuse angle, and is <ised by pushing it forward 

 and cutting off the weeds an inch or less under the surface of the 

 LT. Hind. Hoes are made of different sizes and shapes according to the 

 work which is to be done. When the earth is to be stirred be 

 plants which are very near each other, the hoe is narrow and [minted, 

 so that the smallest weed may be taken out close to the growing plant. 

 When the distance is considerable, the hoe is wide, and SOUP 

 compounded of several hoes, in order to stir a greater width oi 

 at once. 



One of the greatest improvements in practical agriculture has been 

 the introduction of the hoe into the field for every kind of crop. Peas 

 and beans were probably the first crops which were sown in rows for 

 the purpose of hoeing the intervals; potatoes, turnips, and carrots 

 were probably the next, and the good effects produced on these crops, 

 by stirring and hoeing the intervals between the plants, h.ive led to 

 the drilling of even- other kind of produce which is apt to be injured 

 by weeds. Hand-hoeing not having been found sufficiently expeditious 

 on a larp- wale, a hoe has been invented of a larger form to I.e drawn 

 by a hoise. The rows have in consequence been widened, and this has 

 introduced the horse-hoeing husbandry, which, half a century ago. 

 was thought so important a discovery as to receive tl 

 the New Husbandry. The great promoter of this system was J 

 Tull, a gentleman from near Hungerford in Berkshire, who having 

 observed the good effects of stirring the soil around plant*, imagined 

 that tillage might supersede all manuring, 



the soil free from weeds and continually stirred and pulverised, an 

 inexhaiiKtililc fertility might be produced, and successive crops of the 

 same kind might be raised without limit. The horse-hoe was the 

 chief agent in this system, which iiiiit.it.il that of alternate crops and 

 fallows; for the intervals between the rows in which the seed was 

 sown were kept in a constant state of tillage, and thus fallow, d f..r the 

 reception of the seed for the next crop. Although these high cxpecta- 



