the aid of chemistry, "the manufacture of manures may be expected to continue to improve, the supply of manure further augmented and cheapened, and the development of the resources of the soil thereby hastened and increased." Of the branches of natural history, the most useful to agriculturalists are meteorology, "the science of the atmosphere and its phenomena;" botany, "which treats of the structure, functions, properties, habits, and arrangement of plants ;" and zoology, as restricted to the natural history of quadrupeds and insects. The branches of the medical science useful to agriculturalists are comparative anatomy, which treats of the structure of the bodies of animals as compared with that of the body of man; and zootomy, which treats of the structure, and explains the principles of the art of healing the diseases of the domesticated animals.

74. Viewing the general aspect of these sciences as presented to the agricultural pupil, in the definitions just given of them, he must at once observe the advantages he would derive by studying them. It is well observed by Sir John Herschell that, "between the physical sciences and the arts of life there subsists a constant mutual interchange of good offices, and no considerable progress can be made in the one, without of necessity giving rise to corresponding steps in the other. On the one hand, every art is in some measure, and many entirely, dependent on those very powers and qualities of the material world which it is the object of physical inquiry to investigate and explain." It is evident that most farming operations are much affected by external influences. The state of the weather, for example, regulates every field operation, local influences modify the climate very materially, and the nature of the soil generally determines the kind of сгор that should be cultivated. Now the pupil should desire to become acquainted with the causes which give rise to those influences, by understanding the laws of nature which govern every natural phenomenon. The science which investigates those laws, is called Natural Philosophy, which is divided into as many branches as there are classes of phenomena occurring in the earth, air, water, and heavens. Those laws, being unerring in

their operation, admit of absolute demonstration; and the science which affords the demonstration is called Mathematics. Again, every object, animate or inanimate, possesses an individual character, so that it can be identified, and the science which makes us acquainted with its characteristics, is termed Natural History. Farther, every object, animate or inanimate, is a compound body made up of certain elements, of which Chemistry makes us acquainted with their nature and combinations. The pupil thus sees how suitable those sciences are to the explication of the phenomena around him, and their utility will be the more apparent to him, the more minutely each science is investigated.

75. MATHEMATICS.-These are both abstract and demonstrative. Abstract mathematics "treat of propositions which are immutable, absolute truth," not liable to be affected by subsequent discoveries, "but remain the unchangeable property of the mind in all its acquirements." Demonstrative mathematics are also strict, but are "interwoven with physical considerations ;" that is, with subjects that exist independently of the mind's conceptions of them or of the human will; or, in other words still, with considerations in accordance with nature. Mathematics thus constitute the essential means of demonstrating the strictness of those laws which govern natural phenomena. They must, therefore, be first studied before those laws can be understood. Their study tends to expand the mind, to enlarge its capacity for general principles, and to improve its reasoning powers.

76. NATURAL PHILOSOPHY may be divided into five great parts. The first contains the fundamental truths which explain the constitution of the material masses which compose the universe, and the motions going on among them. This last is a department commonly called Dynamics, which relate to force or power. The two great forces of nature, attraction and repulsion, acting upon inert matter, produce the equable, accelerated, retarded, and curved motions which constitute the great phenomena of the universe. The second part explains the peculiarities of state and motion among solid bodies,-a department called Mechanics. The third

explains the peculiarities of state and motion among fluid bodies,-a department called Hydrodynamics, which embraces Hydrostatics or water at rest-Hydraulics, water in motion-Pneumatics, air phenomena-and Acoustics, phenomena of sound or hearing. The fourth part explains the more recondite phenomena of imponderable substances such as Heat, Light, Electricity, Magnetism, and Galvanism. And the fifth part explains the phenomena of the heavens,—a department named Astro

nomy.

77. MECHANICS-Of all the branches into which Natural Philosophy is divided, mechanics have proved the most useful to agriculture. No doubt any labourer may work any machine that answers the purpose it is constructed for; but without a knowledge of this science he cannot understand the principles upon which any machine is constructed, nor can any machine be properly constructed but in accordance with those principles. As implements may be characterised as the right hand of agriculture, mechanical science, in improving their form and construction, may be said to have given cunning to that right hand; for, testing the strength of materials, both relatively and absolutely, it employs no more material in implements than is sufficient to overcome the force of resistance, and it induces to the discovery of that form which overcomes resistance with the least power. Simplicity of construction, beauty of form of the constituent parts, mathematical adjustment, and symmetrical proportion of the whole machine, are now the characteristics of our implements; and it is the fault of the hand that guides them, if field-work is not now dexterously, neatly, and quickly performed. In saying thus much for the science that has improved our implements to the state they now are, when compared with their state some years ago, I do not aver that they are yet perfect; but they are so perfect as to be correct in mechanical principle, and light in operation, though some are not yet simple enough in construction. Many indeed may yet be much simplified in construction; and I consider the machinist who simplifies the action of any useful implement, thereby rendering it less liable to derangement, does as good service to agriculture as the inventor of a new one. Such a result may at all times be expected;

for mathematical demonstration is strictly applicable to mechanics, whether to the principles on which every machine operates, or the form of which it is constructed.

78. Were mechanists to pay more attention to principles, and less to empirical art than they commonly do in several districts, implements would soon assume the form most consonant with the demonstrations of science. As it is, modifications of construction and unusual combinations of parts are frequently attempted by mechanists; and though many such attempts issue in failure, they nevertheless tend to divulge new combinations of mechanical action. It is desirable that every mechanist of implements should understand practical agriculture, and every farmer study the principles of mechanics and the construction of machines, so that their conjoined judgment and skill might be exercised in testing the practical utility of implements. When unacquainted with farming, mechanists are apt to construct implements obviously unsuited to the work they are intended to execute; so that having been put together after repeated alterations, and probably at considerable expense, the makers endeavour to induce those farmers who are no adepts at mechanics to purchase them, and after some unsatisfactory attempts they are put aside. Were farmers acquainted with the principles of mechanics, their discrimination would form a barrier against the spread of implements of questionable utility, and only those find circulation which were obviously simple, strong, and efficient. It is not easy to invent implements possessing all those desirable qualities; but, as they are always exposed to the weather, and the soil is ponderous and uncouth, it is necessary they should be of simple construction. Simplicity of construction, however, has its useful limits. Most farm operations being of themselves simple, they should be performed with simple implements; and all the primary operations, which are simple, requiring considerable power, the simple implements should also be strong; but complicated operations, though stationary, require to be performed with comparatively complicated machinery. Operations that are both complicated and locomotive should be performed with implements producing complicated action by

simple means, in order to avoid derangement of their constituent parts. The solution of this last is a difficult, if not impossible problem, in practical mechanics. The common plough approaches more nearly to its practical solution than any other implement; yet that wonderful implement, executing difficult work by simple means, should yet be so modified in construction, as to give the ploughman a greater command over its motions. These considerations tend to show, that the form and construction of implements, and the circumstances in which they may be used, are still subjects affording scope for mechanical contrivance.

79. In viewing the construction of all machines, an important circumstance to be considered by the pupil is, the resistance among moving parts which arises from friction; and in solid structures, generally, the forms and positions of parts have to be adjusted to the strength of materials, and the strain which the parts have to bear. This consideration should lead the pupil to become acquainted with the strength of materials; and, as a farmer, he will have much need to put such knowledge in practice when he comes to receive the work executed by the carpenter and smith.

80. On considering machines, he should also avoid the common error of supposing that any combination of machinery ever can increase the quantity of power applied. "What an infinity of vain schemes-yet some of them displaying great ingenuity for perpetual motion, and new mechanical engines of power, &c.," exclaims Dr Arnott with reason, in his Elements of Physics, "would have been checked at once, had the great truth been generally understood, that no form or combination of machinery ever did, or ever can increase, in the slightest degree, the quantity of power applied. Ignorance of this is the hinge on which most of the dreams of mechanical projectors have turned. No year passes, even now, in which many patents are not taken out for such supposed discoveries, and the deluded individuals, after selling perhaps their household necessaries to obtain the means of securing the expected advantages, often sink into despair, when their attempts, instead of bringing riches and happiness to their families, end in

disappointment and ruin. The frequency, eagerness, and obstinacy, with which even talented individuals, owing to their imperfect knowledge of the fundamental truths of mechanics, have engaged in such undertakings, is a remarkable phenomenon in human nature."

81. PNEUMATICS.-Next to mechanics, pneumatics is the branch of natural philosophy most useful to the farmer. It "treats of air, and the laws according to which it is condensed, rarified, and gravitates."

82. The atmospheric air surrounds the entire surface of our globe to a height not exceeding 50 miles. Dr Wollaston has shown that, at this elevation, the attraction of the earth upon any air particle is equal to the resistance of the repulsive power of the medium. This height, great

as it may seem, only bears the same relation to the globe as dust of one-tenth of an inch in thickness upon a ball one foot in diameter.

83. The atmosphere presses with considerable force upon the surface of the earth, as well as on every object immersed in it. The weight of 100 cubic inches of air, at 60° Fahrenheit, and the barometer at 30 inches, has been computed, by various authorities, at from 30-199 to 31.10 grains, the average being 30-679. With this weight, and a height of 50 miles, the air exerts a pressure on every square inch of 15 lbs. At this rate its entire weight has been computed at 5,367,214,285,714,285 tons, or equal to that of a globe of lead 60 miles in diameter. The surface of an ordinary-sized man contains 2000 square inches, so that such a person sustains a pressure of 30,000 lbs., which, of course, would be sufficient to crush him to atoms in an instant, were it not that, in obedience to the laws of equal and contrary pressure, this effect is prevented.

84. The air consists in 100 parts of—

and yet their proportions never vary. The powerful agency of the sun's heat and light evolve an abundant supply of oxygen from the luxuriant vegetation in the tropics, whilst the predominant existence of animals in the colder regions affords a large quantity of carbonic acid.

85. Barometer.The gravity of the atmosphere is measured by the well-known instrument, the barometer. Its short column of mercury of 30 inches is as heavy as a column of air of the same diameter of about 50 miles, and of water of about 33 feet. This instrument is placed either in a fixed position or is portable. As the portable barometer is only used to measure altitudes, it need not be here described. The fixed one is made either upright or with a wheel. Whether it is that the long index of the wheel-barometer, being more easily observed than the variations of the column of mercury, makes it more popular among farmers, I know not; but were they to consider of the hindrance occasioned by the machinery required to put the long index in motion, the upright form would always be preferred for accuracy of indication. It is true that the tube of the upright is generally too small, perhaps to save mercury and make the instru

ment cheaper, to the disadvantage of increasing the friction of the mercury in its oscillations in the tube, which supports it above its proper level when falling, and depresses it below it when rising. To obviate this inconvenience, a tap of the hand against the instrument is required to bring the mercury to its proper position. But the objection also applies to the wheel-barometer.

86. The barometer has proved itself a useful instrument. It has proved that the density of the atmosphere decreases rapidly as we ascend. At 3 miles the density is only one-half of the air on the earth's surface, at 6 miles one-fourth, at 9 miles oneeighth, and at 15 miles one-thirtieth. So that the half of the atmosphere is confined to a height of 3 miles, and much the greatest part is always within 20 miles. The depression of the barometer has been found, by experiment, to be one-tenth of an inch for about every 88 feet of elevation; or, more correctly, as given in the table below, by which it will be seen that the density decreases in a geometrical while we ascend the air in an arithmetical progression. Thus, with the barometer, at the level of the sea, standing at 30 inches,

This instrument is thus a correct measurer of the altitudes of places; and on whatever farm observations of the mean height of the mercury are taken, its height above the level of the sea may be correctly ascertained by reference to the above table.

87. No attention should be paid to the words fair, change, rain, commonly engraved on barometers, since the mean elevation of the mercury, in any place, indicates the usual state of the weather

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at that place, whatever be its relative elevation or depression to other places, so that the indications of the weather, as given by the barometer, are to be looked for in its changes and not in its actual height.

88. The cost of an upright barometer, of good workmanship, is from £1, 11s. 6d. to £2, 12s. 6d.; and that of a wheel-barometer from £2, 2s. to £5, 5s. The barometer was invented in Italy by Torricelli, a pupil of Galileo, in 1643.

89. Sympiesometer.-The sympiesometer was invented by Mr Adie, optician in Edinburgh, and answers a similar purpose to the barometer. Its effects are more delicate, being indicated on a longer scale. For the measurement of heights this instrument is convenient, its small size admitting its being carried in the coat-pocket, and not being subject to the same chances of accident as the portable barometer. The height is given in fathoms on the instrument, requiring only one correction, which is performed by a small table engraved on the case. It is stated to be delicately sensible of changes at sea, particularly of gales. Not being brought into general use, though Professor Forbes is of opinion it might be, I need not allude to it farther here.*

90. Sucking-Pump.-The pressure of the atmosphere explains the action of the common sucking-pump. The plunger, by its upward movement, withdraws the air from the chamber of the pump, and the air, pressing on the water in the well, causes it to rise and fill the chamber vacated by the air. The air cannot force the water higher than 33.87 feet. The force-pump acts both by the elasticity and pressure of the air. The pressure causes the water to be lifted to a height not exceeding 33 feet, but the elastic force of the air in the condenser of the force pump causes the water to rise from it to a very considerable height. It is on this principle that the fire-engine causes the water to rise to the roofs of houses.

91. Stomach-Pump. The stomachpump acts as a common pump in withdrawing any liquid from the stomach, and as a condensing syringe in injecting any liquid into it. This is a useful instrument in relieving some of the complaints of live stock.

92. Siphon.-The siphon operates by the pressure of the air, and is useful in withdrawing liquids in a quiescent state from one vessel into another. Water from a quarry may sometimes be removed better by the siphon than any other means. The efficiency of this instrument depends on the greater difference of length of its two limbs.

93. Wind.-Wind is occasioned by a change in the density of the atmosphere; the denser portion moving to occupy the space left by the rarefied. The density of the atmosphere is chiefly affected by the sun's heat raising the temperature of the earth in the tropics to a great degree, and the heated earth, in its turn, rarefies the air above it by radiation. The air, on being rarefied, rises, and is replaced by cold currents from either pole, and these currents being constant constitute the wellknown and useful trade-winds. The great continent of Asia is heated in summer, and the cool air of the Indian seas moves north to occupy the displaced air above the continent. In winter, on the other hand, the water of this ocean, together with the land in the same latitude, are heated in like manner, and the cool currents from the great continent move south to replace the air rarefied by them, and these two currents constitute the half-yearly monsoons.

94. The air over the entire coasts and islands of the ocean is rarefied during the day, and condensed in the night, and these two different states of the air give rise to the daily land and sea breezes.

95. Weather-cock.-The direction of the wind is best indicated by the wind-vane or weather-cock, a very useful instrument to the farmer. It should be erected on a conspicuous part of the steading, that it may be readily observed from one of the windows of the farm-house. Its position on the steading may be seen in the isometrical elevation of that structure. The cardinal points of the compass should be marked with the letters N. E. S. W. The vane should be provided with a ball or box containing oil, which may be renewed when required. There is no neater or more appropriate form for a vane than an arrow, whose dart is always ready to pierce the wind, and whose butt serves as a governor to direct it into the wind's eye. The whole apparatus should be gilt, to prevent rusting.

96. Mr Forster had such a vane erected at his place of residence, which had a small bell suspended from the dart which