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THE 
STUDY OF SCIENCE, 
A FAMILIAR INTRODUCTION 
TO THE 
PRINCIPLES OF SCIENCE AND THE ARTS. 
THE PRACTICAL MECHANIC. 
ANIMAL POWER. 
1. The force of men and animals to put 
machinery in motion and to produce me- 
chanical effects of various kinds, depends so 
much on a variety of complicated circum- 
stances, that it is very difficult to reduce 
it to a fixed standard of measure. The 
circumstances which have the greatest 
share in determining the amount of this 
force are, the natural constitution of 
different individuals of the same spe- 
cies, their acquired dexterity or constant 
practice, the nature of the performance, or 
the muscles brought into action, and the 
duration of the labour or the speed with 
which it is performed. Few of these points 
can be made the direct subject of calculation, 
owing to our total ignorance of the divine 
mechanism by which the living principle is 
made to operate on the animal structure. 
2. Definitions.'] The laborious effort 
\vhich an animal can make for a few in- 
stants, is greatly superior to that which he 
can continue to make for the period of a 
day’s labour. The momentary effort is call- 
ed the absolute force, and the daily effort 
Vac, 'permanent force. In performing the 
daily effort there is a certain speed or velo- 
city of action which produces the greatest 
amount of useful effect ; this is called the 
maximum effect of the permanent force, 
D. Bernouilli considered that the measure 
of the permanent force of man is nearly a 
constant quantity, and that it does not vary 
much either among individuals or in differ- 
ent kinds of labour. Venturoli and others 
doubt this fact, owing perhaps to the mode 
in which this force has been estimated ; but 
we think that Bernouilli is right, and that 
the proposition may be extended to the 
permanent force of other animals ; this 
force, of course, varying with the species. 
The ordinary method of computing me- 
chanical effect or animal power, is by finding 
the 'weight that can be raised to a certain 
height in a given time ; then, the product 
of these three quantities is called the mea- 
sure of the labour or force employed in 
raising the weight, that is, the mechanical 
effect. Force is also measured by d-ynamic 
units i thus, a giving measure of water or a 
given wieght raised through a given space is 
a dynamic unit ; so is the power of an ani- 
mal exerted during a given unit of time. In 
France, a dynamic unit is the weight of a 
cubic metre of water raised to the height of a 
metre, or 2208 lbs. raised 3,281 feet. In 
England, the most common dynamic unit is 
a horse’s power, which is variously estimat- 
ed by engineers. There can be no doubt 
that a practical man must form a more cor- 
rect ideaof the quantity of mechanical power 
expressed by this dynamic unit than by any 
other that could be proposed : because the 
power of the horse is constantly brought 
under his observation, both in the impulsion 
of machinery, and in the transportation of 
loads. 
3. The Dynamoyneter is an instrument 
for measuring the absolute force of men 
and animals. Dynamometers of various 
kinds have been invented ; those of the sim- 
plest construction are the same in princi- 
ple as the spring steel-yard ; others are 
either modifications of this instrument or a 
combination of levers with the spring. The 
Dynamometer of Regnier consists of an 
elliptic spring which is bent either by pres- 
sing it together at the vertices of the minor 
axis, or drawing it apart at the vertices of 
the major axis. In both cases, the sides of 
the spring are made to approach each other 
and thus to move an index which points to 
a graduated semicircle, and shows the 
amount of force which has been applied to 
bend the spring. The semicircle is doubly 
graduated ; the one scale indicates the force 
applied at the vertices of the minor axis ; 
the other scale, that applied at the vertices 
of the major axis. For a further account of 
similar instruments, see Lardner’s Cyclo- 
paedia, vol. V. p. 305. 
4. Human Strength.] The absolute force 
of pressure with the hands was found by 
the dynamometer of Regnier, to be on an 
average equivalent to the weight of 110 lbs. 
The most advantageous and convenient 
position of the arms in pressing, is that of a 
line which makes an angle of 45° with the 
vertical. The right hand commonly presses 
with more force than the left ; and the force 
of both together is equivalent to the sum of 
the forces of each taken separately. 
The absolute force of man in lifting a 
'weight 'with both hands was found by the 
