ANIMAL POWER.] 



APPLIED MECHANICS. 



819 



At present, except for special purposes such as driving 

 a printing-machine, or a turning-la the, where the quantity 

 of work to be done would not warrant the application of 

 costly motive power manual labour at the winch is little 

 used. Engineers of the last generation, with whom 

 human and animal labour was an important considera- 

 tion as a source of motive power, devoted consider- 

 able care to experiments as to the best modes of applying 

 it, and the quantity of power developed. The main re- 

 sult of their deductions was, that in moving machinery, 

 the power of a horse was on the average equivalent to a 

 weight of 33,000 Ibs. , lifted 1 foot high in 1 minute ; 

 and this has accordingly been adopted by engineers as a 

 standard by which all powers, whether of steam-engines, 

 water or wind-mills, are measured. 



The power of a man is about one- fifth of that of a 

 horse ; that is to say, on the average, a man can exert a 

 power equivalent to the lifting of a weight 33,000 Ibs. 

 one foot high in 5 minutes, or 6, 600 Ibs. one foot high in 

 one minute. These estimates are not applicable to a 

 single effort for a short period, but to labour such as 

 could be sustained for hours daily, and continued on 

 successive days. When the power of a man is con. 

 tinuously applied to a winch, it should not be estimated 

 at more than one-half of that given above ; that is to say, 

 3,300 Ibs. raised one foot high in one minute. It is 

 found in practice, that a man working a winch can, for a 

 conaiderable period, move his hand through 120 feet per 

 minute, exerting an average pressure of 30 Ibs. At some 

 parts of the revolution of the winch he exerts more than 

 double this pressure, at other parts less than half ; but, on 

 the whole, the mean pressure may be taken at 30 Ibs. Now, 

 30 X 120, gives a power of 3,600 Ibs. raised one foot per 

 minute, which is rather above the estimate of 3,300, 

 given above. If the radius of the winch be 1 foot, the 

 diameter of the circle in which the hand revolves is 2 

 feet, and its circumference 6f feet ; therefore he makes 

 about 19 revolutions per minute, for 19 X 6f = 120 

 nearly. For a short period, he could turn the winch at 

 the rate of 25 or 30 revolutions per minute, and exert 

 an average pressure at the handle of 40 Ibs. to 60 Ibs. 

 But this high estimate should only be used in calculating 

 when a weight is to be lifted during some minutes, and 

 not when the work is constant. For driving machinery, 

 affording a constant resistance during several hours, the 

 lower estimate of the man's power, viz., 3,300 Ibs., raised 

 one foot high in one minute, should be taken. 



In carrying a load on his back, over level ground, 

 a man can develop a power of about 8,000 Ibs. moved 

 over one foot in one minute. 



In carrying a load up a staircase, his power is equivalent 

 to 2,000 Ibs. lifted one foot high in one minute. 



In dragging a hand cart on level ground, his power is 

 about, 20,000 Ibs. moved one foot in one minute. 



In rowing a boat, the power developed is about 25,000 

 Ibs. moved one foot in one minute. 



For temporary efforts, the following estimates have 

 been made : 



A man can bear, for a short time, standing still, about 

 300 Ibs. weight. 



He can lift vertically about 280 Ibs. 



He can grasp by his hand with a pressure of about 

 100 Ibs. 



The principal applications of manual labour are not 

 those in which great force is required to be developed. 

 Dexterity and skill of manipulation are the qualities 

 chiefly desired in a workman. As more and more pro- 

 gress is made in mechanics, so does the necessity for 

 employing the bodily forces of men diminish. Indeed, a 

 large proportion of the skilled workmen now employed 

 are engaged in merely watching the operation of self- 

 acting machines. Machines are more rigorously true in 

 the work they perform than the hand ; but they are 

 limited to the constant repetition of similar operations. 

 They cannot set their work, adjust their own movements, 

 or vary their efforts, as man can do j but in all these 

 matters they may be controlled by man. It is not our 

 province to inquire into the moral effect produced on 

 workmen, by the extended use of self-acting machinery. 



It is true that much of their corporal labour is saved, and 

 that a vast deal more work is done more economically ; 

 and necessaries and luxuries are thus brought within the 

 reach of millions who would else be deprived of them. 

 At the same time, it must not be forgotten, that the 

 workman is, to a certain extent, degraded into a mere 

 machine, only a little elevated above that, the operations 

 of which he watches and controls. He has no longer to 

 acquire skill and dexterity in his craft machinery does 

 ! the work better than he could ever hope to do ; he has 

 not to think out the easiest and most effective methods 

 of performing it for the machine does a certain kind of 

 work ; the material is placed on it, the power is applied, 

 and he has only to look on. Farther, the kind of work 

 about which he is employed almost exclusively, is of the 

 same unvarying character ; and he is thus subjected to a 

 monotony of occupation, which leaves many intellectual 

 faculties dormant. In former generations, the mill- 

 wright was a man conversant with machinery in general, 

 and with the various operations required in its manu- 

 facture and application. He could make patterns, 

 mould, forge, turn and fashion timber and metal to his 

 uses ; and generally we may say necessarily was a man 

 of intelligence and ingenuity. Now we have pattern- 

 makers, moulders, smiths, turners, fitters, and workmen 

 for attending planing, screwing, slotting, punching, and 

 other machines ; all, in a manner, different trades, re- 

 quiring no versatility of mechanical talent, and not even 

 dexterity of hand. 



No doubt the vastly increased quantity of work is now 

 done in all the better style for this subdivision of labour ; 

 but we fear the moral and intellectual character of the 

 workman is considerably lowered. 



2. NATURAL MOVEMENTS OF AIR. History 

 affords us no information as to the period when, or the 

 race by whom, the movements of the winds and tides 

 were converted into useful mechanical forces. Many 

 savage nations, who for ages could have had no 

 intercourse with people more civilised than themselves, 

 possess vessels that float on the surface of the waters, 

 impelled by the wind or the tidal currents of the sea and 

 rivers, as well as by oars ; and it is probable that the 

 idea of utilising the motion of the wind, or the current 

 of the water, suggested itself to many separate indi- 

 viduals, without any communication among each other. 

 The most simple mode of applying the force of wind is 

 that which is of most general use. the propulsion of 

 vessels on the water. The most casual observation of 

 the natural efiects of wind, shows its greater power on 

 larger surfaces than on small ones ; and a little reflection 

 would offer a reason for tliis, and suggest the extension 

 of surface to receive the pressure of aerial currents, 

 when greater force is sought to be derived from them. 

 A savage floating in his canoe, finds that, by holding up 

 the blade of his oar to catch the favourable breeze, he 

 makes progress without effort ; by holding up two oars, 

 the velocity of his progress is increased ; and by stretch- 

 ing between the oars a mat or skin, so as to iucren.se 

 largely the surface on which the wind can press, the 

 speed of his canoe is proportionally augmented. From 

 the first rude notion of a sail, the steps of transition to 

 the complex rigging and arrangements of canvas in a 

 first-rate man-of-war are easy and obvious ; indeed, in 

 making use of wind-power for propelling vessels, there 

 are only two noints requiring consideration : those are, 

 first, the quantity of the force developed or required ; 

 and, secondly, the direction in which it is to be made to 

 act. The amount of wind-force depends upon the 

 velocity of its movements, and the quantity of surface 

 on which it acts. At first sight it might appear, that by 

 doubling the velocity of the wind, we should double its 

 pressure on a certain area : but this is by no moans the 

 case, for on doubling the velocity, the pressure is quad- 

 rupled ; on tripling the velocity, the pressure is increase' I 

 nine times ; and so on, the pressure being always pro- 

 portioned to the square of the velocity, or the velocity 

 multiplied by itself. On a little consideration, this law 

 becomes obvious, as we will endeavour to show. Let us 

 suppose the air to consist of a mmiber of particles or 



