ESCULENT. 



holly, or sea eryngo (E. inarithmtm), which ' 

 grows on the sandy sea-shore, where it strikes : 

 its long creeping roots eighteen or twenty feet 

 deep into the soil ; the radical leaves are more | 

 or less sheathing, stiff, spinous, three-lobed ; it 

 blows a bright blue flower in July or August. 

 Stem a foot high; root whitish, of a pungent 

 aromatic flavour, with a mixture of mucilage ; 

 herb smooth, glaucous, with an elegant blue 

 tint. The roots, reckoned stimulating and re- 

 storative, are either sold candied or adminis- 

 tered in decoctions variously prepared. 



2. The field eryngo (E. campestre) grows on 

 waste ground chiefly near the sea, and is not 

 so common as the last. It is more bushy and 

 slender, and of a paler glaucous green than the 

 foregoing; radical leaves larger; flowers white 

 or purplish. The leaves of both are somewhat 

 sweet, and of a pungent flavour. 



Mr. Nuttall notices five species of the eryngo 

 or sea-holly, as found in the United States : 

 1. E. Virginianum ; 2. E. virgatum ; 3. E. fceti- 

 dum; 4. E. mjnuticum. His general description 

 of the foregoing is, Stem rather low ; leaves 

 sword-shaped, distinctly margined with setose 

 spines; setae frequently in pairs, &c. ; flowers 

 greenish-white. 5. E. gractle, without spines. 

 Thys last was found in Florida by Dr. Baldwyn. 

 Many other species are submarine ; some exist 

 in inland depressions, and a considerable num- 

 ber grow in arid wastes. (Nuttalfs Genera.') 



ESCULENT (Lat. escidentu*). A term ap- 

 plied to edible roots and plants, as carrots, 

 turnips, cabbages, &c. 



ESPALIERS (Fr. espalier"), in horticulture, 

 are trees trained by lattice-work or other sup- 

 ports on the borders of beds, or as hedges to 

 enclose plots of ground. They may serve to 

 defend in a great measure many tender plants 

 from the inclemencies of wind and weather. 

 The trees chiefly planted for espaliers are 

 apples, pears, and plums. The principal ob- 

 jects aimed at, however, in espaliers, are to 

 expose the foliage and fruit of the plants or 

 trees more perfectly to the light and sun, to 

 prevent the branches from being blown about 

 by the winds, and to economize space by con- 

 fining them within definite limits. (Loud&n's 

 Sut>. Gard. p. 232.) 



ESPARCET. A local name for Sainfoin, 

 which see. 



ESTATE (Fr. afar), in common parlance, is 

 applied to the landed property held by indivi- 

 duals ; and a man is said to be of good or of 

 small estate, according to the magnitude of his 

 landed property. Estates vary exceedingly in 

 size and value, in most parts of England. The 

 largest estate in the kingdom may be worth 

 100,000/., or upwards, a year ; and there are 

 estates of most inferior degrees of magnitude, 

 down to the annual value of 40s. In some 

 counties the property is more, and in others it 

 is less subdivided. 



EUDIOMETER. The name of any appara- 

 tus Or contrivance by which the purity of the 

 air can be tested. It implies a measure of purity, 

 and is chiefly employed to determine the pro- 

 portion of oxygen which the air may contain. 



EVAPORATION is the process by which 

 substances in the fluid or other form are con- 

 verted into vapour and steam. Ice, camphor, 



EVAPORATION. 



carbonate of ammonia, and many other so- 

 lids evaporate readily in the open air. The 

 evaporation of water is, however, the most in- 

 teresting consideration in its relations to agri- 

 culture, as will be more particularly shown 

 when treating of the evaporating qualities of 

 soils, &c. 



Water, when expanded into vapour, is high- 

 ly elastic, and spreads itself by a force of its 

 own. The amount of vapour existing at any 

 time in a given place is determined by the 

 degree of heat present. According, therefore, 

 to the temperature of the water from which 

 the vapour emanates, will be the elastic force 

 and density of the vapour, provided the proces'.* 

 be carried on in an open vessel. 



The pressure of the air and of other vapours 

 upon the surface of water in an open vessel, 

 doej not prevent evaporation of the liquid ; it 

 merely retards its progress. Experience shows 

 that the space filled with an elastic fluid, as air 

 or other gaseous body, is capable of receiving 

 as much aqueous vapour as if it were vacuous, 

 only the repletion of that space with the vapour 

 proceeds more slowly in the former predica- 

 ment than in the latter, but in both cases it 

 arrives eventually at the same pitch. Dr. Dai- 

 ton has very ingeniously proved, that the par- 

 ticles of aeriform bodies present no permanent 

 obstacle to the introduction of a gaseous atmo- 

 sphere of another kind among them, but merely 

 obstruct its diffusion momentarily, as if by 

 a species of friction. Hence, exhalation at 

 atmospheric temperatures is promoted by -the 

 mechanical diffusion of the vapours through 

 the air with ventilating fans or chimney 

 draughts ; though, under brisk ebullition, the 

 force of the steam readily overcomes that me- 

 chanical obstruction. 



The atmosphere has seldom AS much watery 

 vapour as it is capable of .holding, and there- 

 fore the process of evaporation is almost always 

 going on wherever there is a source of mois- 

 ture present. Under certain circumstances, 

 however, evaporation is checked and even 

 suspended. Suppose the temperature of the 

 water to be midway between freezing and boil- 

 ing, viz., 122 Fahrenheit ; also, that the air in 

 contact with it be of the same temperature, but 

 filled with moisture, so that its interstitial spaces 

 are full of vapour of corresponding elasticity 

 with that given off by the water ; it is certain 

 that, under such circumstances, no fresh for- 

 mation of vapour could take place. The air 

 would then be said to be saturated, as it is at 

 times when clothes hung out at common tem- 

 peratures remain without drying, and the 

 grass, leaves, and grain remain soaked in 

 moisture. But the moment a portion of vapour 

 escapes, or is drawn off by condensation into 

 dew, cloud, rain, &c., an equivalent portion of 

 vapour will immediately be enabled to rise, 

 and the process of exhalation or evaporation 

 recommences. The water exhaled at low tem- 

 peratures, that is to say, below the boiling point, 

 is commonly called vapour. When the tem- 

 perature of fresh water in an open vessel, at or 

 near the common level of the sea or tide-water, 

 rises to 212 Fahrenheit, the water begins to 

 boil and evaporate with exceeding rapidity, 

 producing what is commonly termed steain. 



447 



