450 SCIENCE OF AGRICULTURE. Pakt II. 



Chap. I. 

 Manual Labors and Operations. 



2876. The labors and operations of any art can seldom be described with great ad- 

 vantage. Whoever wishes to acquire them should resort at once to the scene of practice : 

 no description, however minute, will teach a man to dig, plough, or mow, equal to a few 

 hours' trial in the field, though a knowledge of the mechanical principles on which the 

 implements and the human machine acts in such operations, wilLafFord some assistance in 

 acquiring them, and in performing them with ease. Our observations shall chiefly be 

 directed to these parts of the subject, and to the most suitable weather and other circum- 

 stances for the performance of the different field labors of the manual kind. We shall 

 arrange these as manual labors common to all arts ; manual operations on the soil ; 

 and mixed manual operations, or such as are performed on the soil, plants, and animals 

 together or connectedly. 



Sect. I. Mechanical Operations common to all Arts of Manual Labor. 



2877. All the operations which man performs with imj)lements or machines, are, as far 

 as his own person is concerned, reducible to lifting, carrying, drawing, and thrusting. 

 Man himself, considered as an engine, derives his power from alterations in the position 

 of his centre of gravity, and he applies it chiefly by his hands, arms, and legs, acting as 

 levers of the third kind. 



2878. Lifting is performed by first stooping or lowering the centre of gravity, and at 

 the same time throwing it to one side. The object being then laid hold of by the hands, 

 the body is raised, and the centre of gravity, in being restored to its true position, acts 

 as a counterbalancing weight to the weight to be raised. The weight retained by the 

 hand is now raised a certain height, never exceeding half that of the man ; if to be 

 raised higher, recourse is had to muscular strength, or the power of the arms to act 

 as levers. 



2879. Carrying. To carry a thing is merely to walk with a greater weight than 

 before, and walking is performed by a series of alternate derangements and adjustments 

 of the centre of gravity, slow or rapid, according as the person may walk or run. Accord- 

 ing to Delolm, the most advantageous weight for a man of common strength to carry 

 horizontally is 112 lbs, ; or, if he returns unladen, 135 lbs, 



2880. Drawing. la this operation, the upper part of the body is thrown forward, so 

 as to act as a power to counterbalance or lift up the body or weight to be moved ; and 

 by joining to this lifting motion the operation of walking, the weight is at once lifted up 

 and drawn along. This compound operation is exemplified in a horse, when straining 

 at a draught in a plough or cart. He first lowers his chest, then raises it, and lastly 

 steps forward. When drawing at ease, the lifting motion is scarcely distinguishable 

 from the progressive one. 



2881. Pushing or thrusting is Tpertormed exactly on the same principles as drawing, 

 and differs from it chiefly in the kind of implement or machine which requires to be 

 employed, all machines which are to be pushed requiring to be attached to the animal 

 machine by parts acting by their rigidity ; whereas those to be drawn may be attached by 

 parts acting by their tenacity merely. 



2882. Wheeling is a mode of carrying materials in which the weight is divided between 

 the axle of the wheel and the arms of the operator. The arms or shafts of the barrow 

 thus become levers of the second kind, in which the power is at one end, and the ful- 

 crum at the other, and the weight between them. The weight is carried or moved on 

 by the continual change of the fulcrum with the turning of the wheel ; and this turning 

 is produced by the operator throwing forward his centre of gravity so as to push against 

 the wheel by means of the moveable axle, &c. The chief obstacles to wheeling are the 

 roughness or softness of the surface to be wheeled on. Where this is firm, there wheel- 

 ing will be best performed with the greater part of the load resting on the axle ; but 

 when soft and deep, the centre of gravity should be nearest the operator, who M'ill find 

 it easier to carry than to overcome excessive friction. Dry weather is obviously prefer- 

 able for this operation. " With wheelbarrows," Dr. Young observes, " men will do 

 half as much more work as with hods. 



2883. All these operations may be varied in quantity, either by a variation in the 

 weight or gravity of the man, or moving power ; or by a variation in the time or rapi- 

 dity of his motions. Thus a heavy man may, in one movement, lift a weight ten times 

 greater than can be done by one of less weight ; but a light man may, by increasing the 

 time of performance, lift the same weight at ten times. A man, who in digging can apply 

 with his feet five cwt. of his weight towards pushing the wedge or blade of the spade into 

 the soil, has an apparent advantage over a lighter man who can only apply three cwt. of 

 mere gravity for that purpose ; but yet the latter may equal the former, by accompanying 

 his power or foot with a proportionate increase of motion. The power in this last case 



