TABLE._Pumps and Hydraulics, Part 1 (of 2)

_Showing the Relation of Time, Space and Velocity._

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1 | 32·16 | 1 | 16·08 | 1 | 16·08

2 | 64·33 | 4 | 64·33 | 3 | 48·25

3 | 96·5 | 9 | 144·75 | 5 | 80·41

4 | 128·66 | 16 | 257·33 | 7 | 112·58

5 | 160·83 | 25 | 402·08 | 9 | 144·75

6 | 193· | 36 | 579· | 11 | 176·91

7 | 225·17 | 49 | 788·08 | 13 | 209·08

8 | 257·33 | 64 | 1029·33 | 15 | 241·25

9 | 289·5 | 81 | 1302·75 | 17 | 273·42

10 | 321·66 | 100 | 1946·08 | 19 | 305·58

| | | | |

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Experience has shown that the measurement of all physical quantities

may be expressed in terms of three fundamental magnitudes. Those

commonly chosen for this purpose are _time_, _length and mass_ _or

quantity of matter_. It may be assumed that our ideas of time and space

are sufficiently exact for all practical purposes. The subject of

matter, however, requires more particular consideration. Of the three

magnitudes named, matter alone is directly cognizable by the senses,

and invested with a variety of interesting properties.

For present purposes matter may be defined as anything that can be

weighed, and the quantity of matter as proportional to its weight;

_i. e._, its attraction towards the earth. The _weight_ of a body is

the force it exerts in consequence of its gravity, and is measured by

its mechanical effects, such as bending a spring. We weigh a body by

ascertaining the force required _to hold it up_, or to keep it from

descending. Hence, weights are nothing more than _measures of the force

of gravity_ in different bodies.

Again, Gravitation, the most feeble of physical actions between

small masses, is almost imperceptible; yet it is an energy abundant

in proportion to the quantity of matter in the universe, and fully

competent, by its gradual condensing agency, to account for the

origination of planetary systems and their movements. It is not

strange, therefore, that by some physicists this energy is supposed

to be the beginning of that of which all other forms of force are

residues or metamorphoses. Gravity is the name especially given to

its terrestrial manifestations. _A particle or body without a sphere

or spheroid, solid or hollow, is attracted to the center of the mass

of such body; within a hollow sphere, it will remain at rest at any

point._ At different depths below the earth’s surface, a body will be

attracted with a force diminishing as the distance from its center

decreases. The slight variation in the gravitating force of the same

falling body at different heights is in practice usually disregarded.

The weight of a body, as the measure of its gravitating tendency,

must vary both with mass and with the force acting on it; hence, from

the form of the earth, the same body at the sea level _will weigh

less and less as it is removed from either pole toward the equator_.

An elevation above the sea level gives a like result. A stone falls

through a less distance in a given time on a mountain than in the

valley below, less at the equator than at either pole. The loss of

weight in these cases cannot be tested by lever scales, in which

this loss is equal on both sides; but it may be by the spring

balance, in which bodies are weighed by the pull they exert against

the elasticity of a coiled wire. The effect of centrifugal force,

increasing from the pole to the equator, co-operates with increasing

removal from the earth’s center to lessen weight; the result of the

combined action of these two causes is, that a body weighing 195 lbs.

at either pole will weigh but 194 over the equator. _The line of a

falling body, called also the line of direction_, is interesting as

being that direction in space at any point of the earth’s surface

with reference to which all other directions are named, and by which

they are to be determined.

A few points remain to be named. _The flow of water is the result

of the force of gravity_; the importance of this fact and its wide

influence cannot be over stated; the gently falling dew, the mighty

currents in the unfathomable depths of the ocean, as well as the

rivulet merrily falling over the rocks to a lower level are all subject

to the laws of terrestrial gravity.

The upper surface of a liquid in a vessel exposed to the atmosphere is

called _the free surface_ and is pressed downwards by the air under

about 15 lbs. pressure per square inch. The free surface of a small

body of a perfect liquid, at rest, is horizontal and perpendicular to

the action of gravity although in large bodies of liquid, as lakes and

ponds, the free surface is spherical, assuming the curvature of the

earth’s surface.