772. _What is attraction?_
Attraction is the tendency of bodies to _draw near to each other_.
It is called _attraction_, from two Latin words signifying _drawing
towards_.
773. _How many kinds of attraction are there?_
There are five principal kinds of _attraction_:--
1. The attraction of _gravitation_.
2. The attraction of _cohesion_.
3. The attraction of _chemical affinity_.
4. The attraction of _electricity_.
5. And _capillary attraction_.
[Verse: "Behold, the nations are as a drop of a bucket, and are
counted as the small dust of the balance: behold, he taketh up the
isles as a very little thing."--ISAIAH XL.]
774. _Why do all bodies heavier than the air fall to the earth?_
Because they are influenced by the _attraction of gravitation_, by
which all bodies are drawn towards _the centre of the earth_.
775. _Why do bodies lighter than the air ascend?_
Because the air, being a denser body, _obeys the law of attraction_,
and in doing so _displaces lighter bodies_ that interfere with its
gravitation.
776. _Why do fragments of tea, and bubbles floating upon the surface of
tea, draw towards each other, and attach themselves to the sides of the
cup?_
Because they are influenced by the _attraction of cohesion_.
_Cohesion._--The act of sticking together.
777. _Why will a drop of water upon the blade of a knife leave a dark
spot?_
Because the _iron of the knife attracts the oxygen of the water_, by
_chemical affinity_; and the two substances form a thin coating of
_oxide of iron_.
_Affinity._--Attraction between dissimilar particles through which
they form new compounds.
778. _Why do clouds sometimes move towards each other from opposite
directions? and_
779. _Why do light particles of matter attach themselves to sealing
wax, excited by friction?_
Because they are moved by the _attraction of electricity_.
780. _Why will a towel, the corner of which is dipped in water, become
wet far above the water?_
Because the water is conveyed up through the towel, by _capillary
attraction_. The atoms of the water are attracted by the _threads of
the towel_, and drawn up into the _small spaces between the threads_.
_Capillary._--Resembling a hair, small in diameter.
[Verse: "He stretcheth out the north over the empty place, and
hangeth the earth upon nothing."--JOB XXVI.]
781. _Why do small bodies floating upon water move towards larger ones?_
Because the attractive power of a _large body_ is greater than that of
_a small one_. As each atom of matter has inherent power of attraction,
it follows that a _large aggregation of particles_ must attract in
proportion to the number of those particles.
782. _Why do clouds gather around mountain tops?_
Because they are _attracted by the mountains_.
783. _Why would a piece of lead tied to a string, and let down from a
church steeple, incline a little from the perpendicular towards the
church?_
Because the _masses of stone_ of which the church is built would
_attract the lead_.
784. _How can man weigh the earth?_
By observing what is called the _deflection_ of small bodies _when
brought within given distances of larger bodies_, the degree of
attraction _exercised by the large body upon the smaller one_ becomes
known. This attraction of the _large body_ exercised over the _smaller
body_ is an opposing influence, _acting against the earth's attraction
of the small body_, which is drawn out of its course: it constitutes a
_natural balance between the influence of the earth and another body,
acting in opposition to it_. Founded upon these, and some other data,
man can weigh the earth, and give a morally certain result!
_Deflection_.--The act of turning aside.
785. _How can man weigh the planets?_
The planets exercise as certain an influence upon each other _as do
two pieces of wood floating upon a basin of water_. As the planetary
bodies fly through their prescribed orbits, _and approach nearer to, or
travel further from, each other_, they are observed to _deviate_ from
that course which they must have pursued _but for the increase or the
decrease of some influence of attraction_. By making observations _at
various times_, and by comparing _a number of results_, it is possible
_to weigh any planetary body, however vast, or however distant_.
[Verse: "Is not God in the height of the heaven? and behold the
height of the stars, how high they are?"--JOB XII.]
786. _How can man measure the distances of the planets?_
By making observations at _different seasons of the year_, when the
earth is in _opposite positions in her orbit_; and by recording, by
_instruments constructed with the greatest nicety_, the _angle of
sight_, at which the planetary body is viewed; by noticing, also, _the
various eclipses_, and estimating _how long the first light after an
eclipse has ceased_ reaches the earth, it is possible to estimate the
_distances_ of heavenly bodies, _no matter how far in the depths of the
universe those orbs may be_.
787. _What are the opinions founded upon estimates respecting the
magnitude of the sun?_
The _diameter_ of the _sun_ is 770,800 geographical miles, or 112 times
greater than the diameter of the earth; its _volume_ is 1,407,124
times that of the earth, and 600 times greater than _all the planets
together_; its _mass_ is 359,551 times greater than the earth; and 738
times greater than that of _all the planets_. A _single spot_ seen upon
its surface has been estimated to extend over 77,000 miles in diameter,
and a _cluster of spots_ have been estimated to include an area of
3,780,000 miles.
788. _What is the weight of the earth?_
The earth has a _circumference_ of 25,000 miles, and is estimated to
_weigh_ 1,256,195,670,000,000,000,000,000 tons.
789. _What is the specific gravity of a body?_
It is its weight estimated _relatively to the weights of other bodies_.
790. _What determines the force with which bodies fall to the earth?_
Generally speaking, their _specific gravity_, which is proportionate to
the density, or _compactness of the atoms_ of which they are composed.
791. _Why does a feather fall to the earth more gradually than a
shilling?_
Because the _specific gravity_ of the feather and of the shilling is
_relative to that of the air_, the medium through which the feather and
the shilling pass. If there were _no air_, a shilling and a feather
dropped at the same time from a height of forty miles, _would reach the
earth at the same moment_.