« ПредыдущаяПродолжить »
them seem less easy to be accounted for: such are joyns, joynt, joyntly, enjoyned; set, for sit; setting, for fitting ; complane, dispare, waive.
Upon the whole, were we to judge of this piece by the Horatian standard, we should be obliged to conclude, that altho' it
where abounds in the Utilé, as may be seen by this small specimen of it; yet it hath very little in it of the Dulcé,
Aftronomy explained upon Sir Isaac Newton's Principles, and
made easy to those who have not ftudied Mathematics. By James Ferguson Sold by the Author, at the Globe, opposite Cecil-street in the Strand. 4to. 155. HERE is scarce any study that seems better calculated
to enlarge the mind, to raise it above mean and vulgar prejudices, and to fill it with sentiments of the most profound reverence towards the ORIGINAL PARENT MIND, the Father of the Universe, the Ever-flowing Fountain of Good, than the study of Astronomy. Whoever, therefore, employs his pen in conveying some general knowlege of this useful branch of science, to those who are unacquainted with mathematical calculations, and who have neither leisure nor capacity to tread the dry and intricate paths of Geometry, certainly deserves the thanks of the public. Among the vast numbers, indeed, of those who are engaged in literary pursuits, there are but few who are qualified to treat subjects of this kind in an easy and familiar manner; to strip them of that stiff and uncouth dress in which they have generally made their appearance, and to bring them down to the level of vulgar capacities.
The Author of the work now under consideration appears to be very well qualified for the task he has undertaken; his ideas seem to be clear and distinct ; his language is easy and perspicuous; and his illustrations are ingenious and pertinent. He has divided his performance into fixteen chapters, the first of which contains a brief description of the Solar System, the truth of which is demonstrated in the second; and the appearances resulting from the earth's motion described. In treating of the earth's motion, he endeavours to illustrate it in the following manner.
. Let us imagine,' says he,' a prodigious large room of a ! round form, all hung with pictures of men, women, birds,
• beasts, and fishes; the floor covered with water deep enough
to carry a boat with a person sitting still in it; and that there • is a great taper burning in the midst of the room, the flame
being of equal height with the person's head from the wa
ter. If a diver under the boat, unknown to, and unperceiv• ed by, this person, should turn it gently and equally round • and round, as on an axis, giving it at the same time a flow • progressive motion round the taper, the same way, but so as
to turn it three hundred and fixty-five times round its axis while it went once round the taper ; to the person in the boat the whole room and taper would seem to go round the contrary way every time the boat turned round; the flame
would appear to change its place gradually among the pic• tures, so as to make a tour round the room among them in
every revolution of the boat round the taper. And in that ( time the observer would be turned so much sooner towards
any particular piąure than to the taper, in each turning of the boat, that the whole room and pictures would seem to
go once more round him than the taper did. The applica• tion is obvious, if we imagine the pictured room to repre« sent the visible heavens fet all round with stars ranged in dif
ferent constellations, the taper the sun, and the boat the ( earth.'
In the third chapter he refutes the Ptolomaic system; and explains briefly the motions and phases of Mercury and Venus. In the fourth he treats of the physical causes of the motions of the planets, of the excentricities of their orbits, the times in which the action of gravity would bring them to the sun, and of the ideal problem of Archimedes for moving the earth.
The quick motions of the moons of Jupiter and Saturn round their primaries, demonstrate, he tells us, that these two planets have stronger attractive powers than the earth. For,' says he, the stronger that one body attracts another, the greater must be the projectile force, and consequently the
quicker must be the motion of that other body, to keep it « from falling to its primary or central planet. Jupiter's se
cond moon is one hundred and twenty-four thousand miles • farther from Jupiter than our moon is from us; and yet this • second moon goes more than eight times round Jupiter ' whilst our moon goes only once round the earth. What
prodigious attractive power must the sun then have, to draw • all the planets and satellites of the system towards him, and • what an amazing strength must it have required at first, to
put all these planets and moons in motion! Amazing to
even by Almighty Power; and that the Deity must there
ús, because impollible to be effected by the strength of all the people in an unlimited number of worlds, as will appear by the following article; but it is nothing to the Almighty, whose Planetarium takes in the whole universe.
It is reported of Archimedes, (falsely I believe) that he faid he could move the earth, if he had any place at a di* ftance from it to fix a prop for his lever. Now, suppose a
man could press upon the end of a lever the force of two hundred pounds, and that the weight of the earth be *399,784,700,118,074,464,789,750; if we imagine the earth to be placed at one end of the lever, at the distance of fix thousand miles from the prop or center of motion, then
must the person or power be applied to the other end of the ** lever, at the distance of 11,993,541,003,542,233,943, ** 692,500 miles from the earth to sustain it; which is 15,569,
745,951,035,731 times the mean distance of Saturn from
the earth. And, to raise the earth but one mile, the power * must move through the space of 1,998,923,500,590,322;
323,948 miles : consequently, if Archimedes, or the power, could move as fwift as a cannon-ball, i. e. four hun: dred and eighty miles every hour, he would require 44,9633 540,000,000 years to raise the earth one inch,
Our Author proceeds now to offer some reflections upon gravity.
The sun and planets mutually attract each other : the power by which they do so, we call Gravity. But whether
this power be mechanical or not, is very much disputed. * We are certain that the planets disturb one another's moti
ons by it, and that it decreases according to the squares of • the distances of the sun and, planets; as light, which is * known to be material, likewise does. Hence Gravity should
seem to arise from the agency of some subtile matter issuing from the sun and planets, and acting like all mechanical causes by contact. But, on the other hand, when we consider, that the degree of it is exatly in proportion to the quantities of matter in those bodies, without any regard to their bulks òr quantity of surface, acting as freely on their
internal as external parts, it seems to surpass the power of he mechanism; and to be either the immediate agency of the * Deity, or effected by a law originally established and im
prefied on all matter by him. But fome affirm, that matter being altogether inert, cannot be impressed with any law,
fore be constantly impelling the planets towards the sun, and moving them with the same irregularities and difturb
ances which Gravity would cause, if it could be fupposed “to exift. But, if a person may venture to publish his own
thoughts, (and why thould not one as well as another ?) . it seems to me no greater abfurdity, to suppofe the Deity
capable of fuperadding a law, or what law he pleafes, to matter, than to fuppose him capable of giving it existence
The manner of both is equally inconceivable to
but neither of them imply a contradiction in our ideas ; • and what implies no contradiction, is within the power of • Omnipotence. Do we not see that a human creature can
prepare a bar of steel, so as to make it attract needles and « filings of iron; and that he can put a stop to, and again ..call forth that power or virtue as often as he pleases ?
Το fay that the workman infuses any new power into the bar;
is saying too much ; fince the needle and filings to which he • has done nothing, re-attract the bar. And from this it ap
pears, that the power was originally impreft on the matter • of which the bar, needle, and filings are composed; but 6-does not feem to act until the bar be properly prepared by r the artificer: fomewhat like a rope coiled up in a fhip, ( which will never draw a boat, or any other thing, towards s-her, unless one end be tied to her and the other end to that
which is wanted to be hauled 'up; and then it is no matter • 'which end of the rope the failors pull at, for it will be
equally stretched throughout, and the thip and boat will * move towards one another. To say that the Almighty has
infused no such virtue or power into the materials which s-compose the bar, but that he waits till the operator be plea• fed to prepare it by due position and friction ; and then, ! when the rieedle or filings are brought pretty near the bar,
the Deity preffes them towards it, and withdraws his hand whenever the workman, either for use, fancy, or whim,
does what appears to him to destroy the action of the bar, « seems quite ridiculous and trifling; as it fuppofes God to do ( what would be below the dignity of any rational man to be employed about.
" That the projectile force was at first given by the Deity, " is evident. For, since matter can never put itself into mo' tion, and all bodies may be moved in any direction whatso
ever; and yet all the planets, both primary and secondary, "'move from west to eait, in planes nearly coincident; whilft
the comets move in all directions, and in planes so different * from one another, these motions can be owing to no me"chanical cause or necessty, but to the free choice and power • of an intelligent Being.
• Whatever Gravity be, it is plain that it acts every mo? "ment of time: for should its action cease, the projectile « force would that very moment catry off the planets in straight • lines from those parts of their orbits where Gravity left " them. But, being once put into motion, there is no oc• cafion for any new projectile force, unless they meet with • some resistance in their orbits; nor for any mending hand, ' unless they disturb one another by their mutual attractions.
• It is found, that there are difturbances among the planets « motions, arising from their mutual attractions, when in the ' same quarter of the heavens: and that our years are not al
ways precisely of the same length. Besides, there is reafort < to believe that the moon is somewhat nearer the earth now • than she was formerly; her periodical month being shortet
than it was in former ages. For, our Astronomical Tables, • which, in the present age, shew the times of folar and lu.nar eclipses to great precision, do not answer fo well for
very ancient eclipses. Hence it appears, that the moon does • not move in a medium void of all resistance; and therefore
her projectile force being a little weakened, whilst there is nothing to diminish her Gravity, she must be gradually ap
proaching nearer the earth, describing less circles round it . in every revolution, and finishing her period sooner, al
though her absolute motion, with regard to space, be • not so quick as formerly. Hence, she must come to the • earth at last; unless that Being, which gave her a sufficient
projectile force at first, adds a little more to it in due time. • And, as all the planets move in spaces full of æther and
light, which are material substances, they too must meet with some resistance. And, therefore, if their gravities are neither diminished, nor their projectile forces increased;
they must necessarily approach nearer and nearer the sun; ' and at length fall upon and unite with him.
• Here we have a strong philofophical argument against the ' eternity of the world. For, had it exifted from eternity; ' and been left by the Deity to be governed by the combined « actions of the above forces or powers, generally called laws, < it had been at an end long ago.
And if it be left to them; it must come to an end. But we may be certain, that it
will last as long as intended by its Author, who ought no 6 more to be found fault with for framing so perishable a work; • than for not making our bodies immortal.'
In the fifth chapter our Author treats of light; its proposé tional quantities on the different planets ; its refractions in wat ter and air: the Atmos, here, its weight and properties: the