Chapter XIX: Part 19

In the Rev. Mr. Vince’s great work, entitled, _A Complete System of
Astronomy_, (and contained in “A Treatise on Practical Astronomy,” at
the end of the second volume of that work,) is an entire chapter on
“_Hadley’s Quadrant_;” giving a particular description of the
instrument, with rules for the computations from the observations and
illustrations of them by examples. In this Treatise, the author says,
that the instrument took its name from the “inventor,” John Hadley,
Esq. and observes, that not only the science of navigation is greatly
indebted, to this “incomparable instrument,” but such are its various
uses in astronomy, that it may not improperly be called “a portable
observatory.” Mr. Vince further observes, that in the year 1742, about
ten years after Mr. Hadley’s invention (for so he styles it) was
published, a paper in Sir Issac Newton’s own hand-writing was found
among Dr. Halley’s papers, after the Doctor’s death, containing a
figure and description of an instrument (referring to _Philos.
Transactions_, No. 465,) not much different in its principle from this
of Hadley. He adds, that as Dr. Halley was alive when Mr. Hadley’s
instrument was shewn to the Royal Society, and he took no notice of
this paper of Sir Isaac Newton, it is probable he did not know there
was such an one. In another part of his work (under the head of _The
History of Astronomy_, vol. ii. p. 280.) Mr. Vince asserts, that the
first person who formed the idea of making a Quadrant to take angles
by reflection, was Robert Hook; and he was born in 1635. On the whole,
however, the learned author draws this conclusion:—“Both Sir Isaac
Newton and Mr. Hadley therefore seem entitled to this invention.”

Mr. Lalande, speaking of this instrument, says: “Le Quartier de
Reflexion, exécuté en 1731 par Hadley, a donné un moyen facile de
mesurer les distances sur mer, à une minute pris, aussi bien
determiner le lieu de la Lune en mer.” See his _Astronomie_, vol. iii.
p. 654.

From these facts, and a careful examination of the papers themselves,
here quoted and referred to, the scientific reader will be enabled to
decide upon the true merits of the controversy that has so long
subsisted, concerning the respective claims of Godfrey and of Hadley,
to the invention of the instrument that bears the name of the latter.

Before this subject is dismissed, however, it will not be deemed
improper to add, that the late Dr. John Ewing communicated to the Am.
Philosophical Society an account of an Improvement in the construction
of (what he terms) “Godfrey’s double reflecting Quadrant,” which he
had discovered in the spring or summer of the year 1767: this will be
found in the first volume of the Society’s Transactions. In the
conclusion of this communication, Dr. Ewing says:—“This improvement of
an instrument, which was first invented and constructed by Mr. Godfrey
of this city, and which I do not hesitate to call the most useful of
all astronomical instruments that the world ever knew, I hope will
make it still more serviceable to mankind.”

This communication to the Society by Dr. Ewing, was made in the year
1770. In one concerning the comet of that year, and made by Dr.
Rittenhouse about the same time, the instrument to which Dr. Ewing’s
improvement applies, is called Hadley’s Quadrant: but perhaps Dr.
Rittenhouse so named it, in conformity to common usage.

-----

But when I consider, that _luxury_ and her constant follower _tyranny_, who have long since laid in the dust, never to rise again, the glories of Asia, are now advancing like a torrent irresistible, whose weight no human force can stem, and have nearly completed their conquest of Europe; luxury and tyranny, who by a vile affectation of virtues they know not, pretend at first to be the patrons of science and philosophy, but at length fail not effectually to destroy them; agitated I say by these reflections, I am ready to wish—vain wish! that nature would raise her everlasting bars between the new and old world; and make a voyage to Europe as impracticable as one to the moon. I confess indeed, that by our connections with Europe we have made most surprising, I had almost said unnatural, advances towards the meridian of glory; but by those connections too, in all probability, our fall will be premature. May the God of knowledge inspire us with wisdom to prevent it: let our harbours, our doors, our hearts, be shut against luxury. But I return to my subject, and will no longer indulge these melancholy thoughts.

Some have observed, that the wonderful discoveries of the microscope ought to go hand in hand with those of the telescope; lest whilst we contemplate the many instances of the wisdom and power of divine Providence, displayed in the great works of creation, we should be tempted to conclude that man, and other less important beings of this lower world, did not claim its attention. But I will venture to affirm, without at all derogating from the merits of those who have so greatly obliged the world with the success of their microscopical enquiries, that no such danger is to be apprehended. Nothing can better demonstrate the immediate presence of the Deity in every part of space, whether vacant or occupied by matter, than astronomy does. It was from an astronomer St. Paul quoted that exalted expression, so often since repeated; “_In God we live, and move, and have our being_.” His divine energy supports that universal _substratum_ on which all corporal substances subsist, that the laws of motion are derived from, and that wings _light_ with angelic swiftness.

If the time would permit, how agreeable the task to dwell on the praises of Astronomy: to consider its happy effects as a science, on the human mind. Let the sceptical writers forbear to lavish encomiums on their cobweb Philosophy, liable to be broken by the smallest incident in nature. They tell us it is of great service to mankind, in banishing bigotry and superstition from amongst us. Is not this effectually done by Astronomy? The direct tendency of this science is to dilate the heart with universal benevolence, and to enlarge its views. But then it does this without propagating a single point of doctrine contrary to common sense, or the most cultivated reason. It flatters no fashionable princely vice, or national depravity. It encourages not the libertine by relaxing any of the precepts of morality; nor does it attempt to undermine the foundations of religion. It denies none of those attributes, which the wisest and best of mankind, have in all ages ascribed to the Deity: Nor does it degrade the human mind from that dignity, which is ever necessary to make it contemplate itself with complacency. None of these things does Astronomy pretend to; and if these things merit the aim of Philosophy, and the encouragement of a people, then let scepticism flourish, and Astronomy lie neglected; then let the names of Berkeley, and Hume, become immortal, and that of Newton be lost in oblivion.

I shall conclude this part of my discourse with the words of Dr. Barrow—It is to Astronomy we owe “that we comprehend the huge fabric of the universe, admire and contemplate the wonderful beauty of the divine workmanship, and so learn the invincible force and sagacity of our own minds, as to acknowledge the blessings of heaven with a pious affection.”

I now come, in the last place, to point out some of the defects of Astronomy at this day. Which I am induced to undertake by the hopes I entertain that some of those defects may be removed under the auspices of this society, and of you my fellow citizens, who have so zealously promoted its institution. “The advantages arising from Astronomy, the pleasure attending the study of it, the care with which it was cultivated by many great men among the ancients, and the extraordinary attention paid to it in Europe by the present age,” all contribute to recommend it to your protection, under which we have the best reason to expect that it will flourish.

The mildness of our climate and the serenity of our atmosphere, perhaps not inferior to that of Italy, and likewise our distant situation from the principal observatories in the world (whence many curious phænomena must be visible here that are not likely to be observed any where else) are so many circumstances greatly in our favour.

And I trust there will not be wanting men of genius, to arise in this new world, whose talents may be particularly adapted to astronomical enquiries. Indeed I am persuaded that nature is by no means so nigardly in producing them, as we are apt to imagine. Some are never tempted forth from obscurity, some are untimely snatched away by death, a striking instance whereof we have in Horrox; and many are accidentally led to other pursuits.

The Astronomy of comets is still in its infancy; not that the attention of the learned and ingenious has at all been wanting for more than a century past; but because it will necessarily require many ages to bring it to perfection. I wish we were in a condition to promote it in some degree, by carefully observing such comets as may appear. As yet we scarce dare affirm that any one has or will return a second time. It has never, that I know of, been certainly proved by observation, that a comet has descended within a parabolic orbit, and until that is done we have only a coincidence of periods and orbits (none of which have been very precise) to depend on for their return. Far less are astronomers able to determine the changes that may, and probably do, happen in their orbits[A36] and velocities in every period, so as to predict their nearer or more remote approach to the earth or any planet. Whether their business be to repair or destroy, whether they are worlds yet in formation or once habitable worlds in ruins; whether they are at present habitable and regular attendants of our Sun only, or whether they are the vast links that connect the distant parts of creation by surrounding more suns than one, we know not.

-----

Footnote A36:

This I know has been pretended to. But it is easy to make geometrical
conclusions come out as we would have them, when the data they are
founded on, are so uncertain that we may chuse them as suits our
purpose.

-----

If we descend to the Planetary System, there are still many things wanting to compleat Astronomy.

The orbits of the primary planets have at one time been supposed moveable with various irregularities, at other times fixed and permanent. It seems now generally granted, that according to the theory of gravity they must change their situations; yet not long since, some great astronomers warmly contended that this change was altogether insensible.

According to the best tables we now have, the planes of the orbits of Jupiter, the Earth and Mercury are immoveable, though the orbits themselves have a progressive motion in their planes. On the contrary, the poles of the orbits of Saturn, Mars and Venus are supposed to revolve about the poles of the earth’s orbit, with such velocities as at present nearly reconcile calculation to appearances. But there is good reason to apprehend that such a supposition is not true in fact, and a mistake in this matter will have some important consequences. More probable is it, that the poles of the orbits of all the planets, the earth not excepted, revolve about some common centre. The several quantities of these motions, I am confident, are to be had from observation, and not from theory alone. If such a motion of the earth’s orbit be admitted, it will account for the diminution[A37] of the obliquity of the ecliptic; which seems now incontestible; and that in whatever manner we divide the forces producing such motion, amongst the two superior planets and Venus, or even amongst all of them. And I should suspect the further diminution of obliquity, from this cause, will amount to about one degree and an half.

-----

Footnote A37:

This circumstance tends gradually to lessen the variety of the
seasons.

-----

But as Astronomy now stands, it seems doubtful whether this change is owing to a deviation in the diurnal or annual motion of the earth; which introduces a very disagreeable uncertainty in conclusions drawn from some nice and useful observations.

The Lunar Astronomy has been brought so much nearer to perfection, by the celebrated MAYER,[A38] than could have been expected, that I shall mention no deficiency in it, but this. We do not certainly know whether that apparent acceleration of the moon’s motion, which Mayer with other great astronomers has admitted, ought to be attributed to a real increase of velocity in the moon, or to a diminution of the earth’s diurnal motion. If to the former, the destruction of this beautiful and stupendous fabric, may from thence be predicted with more certainty than from any other appearance in Nature: But if to the latter, it may be prettily accounted for, by Dr. Halley’s ingenious hypotheses concerning the change of variation in the magnetical needle. The Doctor supposes the external crust or shell of the earth to contain a nucleus detatched from it, and that the impulse which first caused the diurnal motion, was given to the external parts, and from thence in time communicated to the internal nucleus, by means of an intervening fluid; but not so as perfectly to equal the velocity of the superficial parts of the globe. Whence it will follow, that the external shell of the earth is still communicating motion to the internal parts, and losing motion itself proportionably. The diurnal motion must therefore become slower and slower, yet can never be retarded, by this cause, beyond certain limits; nor can we conceive that any inconvenience will follow.

-----

Footnote A38:

This was Tobias Mayer, who was born at Marbach in the principality of
Wurtemberg, in the year 1723: he rendered himself celebrated in
astronomy, by having calculated the best tables of the moon, and by an
excellent catalogue of stars. He died at Gottingen in 1762, at the age
of thirty-nine years. W. B.

-----

There is another physical question relating to the moon, which to me appears extremely curious; it is this—Whence is it that the moon always turns the same side to us? or, which is the same thing, How comes the moon’s rotation on her axis, and her monthly revolution about the earth, to be performed in the same time? None I believe will suppose it to be accidental, nor will the astronomer be easily satisfied with a final cause. Was it not originally brought about by a natural cause which still subsists? Can the attraction of any foreign body change a rotatory motion into a libratory one, and a libratory motion into rest, in spaces so very free from all resistance as those wherein the planets move? There are other defects in Astronomy that are purely optical. Removing of those, depends on the further improvement of telescopes, or rather on the more judicious use of them, at times and places the most favourable.

In speaking of telescopic discoveries I purposely reserved those made on Venus for this place, because they are still uncertain. Burratini in Poland first discovered spots in Venus, then Cassini in Italy; and afterwards Bianchini got a sight of them. But from all their observations it is uncertain, whether Venus revolves on its axis once in 23 hours, or once in 24 days. Perhaps it does neither. Nor is their determination of the axis’ situation much more satisfactory. These spots on Venus are not to be seen but through an excellent telescope and a pure atmosphere.

In the year 1672 and 1676 Cassini saw a small star near Venus, which he thought might be a satellite attending on her. It appeared to have the same phase with Venus. In 1740 Mr. Short with a telescope of 16 inches saw a small star at the distance of ten minutes from Venus, which from its apparent shape he likewise thought might be a satellite. And in 1761 Mr. Montaigne, in France, saw what he took to be the satellite of Venus, on the 3d, 4th, 7th and 11th of May.[A39] But whether Venus has a satellite or not, must still be left amongst the doubtful things of Astronomy.

-----

Footnote A39:

It may happen that any of the planets, about the time they become
stationary, shall describe a loop about some small fixed star, in such
manner as might be easily mistaken for the star making part of a
revolution about the planet. This I suspected to have been the case
with the above observation of Montaigne. But the times set down do not
confirm the suspicion.

-----

The spots on the sun, and those on the surfaces of several planets, have been many years observed without our approaching any nearer towards discovering their nature and cause. Dr. Wilson of Glasgow, has lately succeeded in advancing one step at least, with respect to those of the sun. He has proved from observation that those spots are vast cavities, whose bottoms lie far below the general surface of the sun, and whose sloping sides form the border which we generally see surrounding them. If I should venture to add one conjecture of my own, to those of this ingenious gentleman, I would suppose that those prodigious cavities in the surface of the sun, some of them capable of containing half our earth, are not repeatedly formed by unaccountable explosions of a semifluid substance, but permanent and solid, like the cavities within the moon. And that it is the dark matter sometimes lodging in them, that distinguishes them, and is only accidental.

The diurnal rotations of Saturn and Mercury are yet unknown; but when further improvements shall be made in the art of using telescopes, this circumstance will hardly escape the vigilance of astronomers.

These are a few of the many things that are still left to the industry of the ingenious in this science.

But if all higher and more sublime discoveries are not reserved for us in a future and more perfect state; if Astronomy shall again break those limits that now seem to confine it, and expatiate freely in the superior celestial fields; what amazing discoveries may yet be made amongst the fixed stars! That grand phænomenon the Milky-Way seems to be the clue that will one day guide us. Millions of small stars compose it, and many more bright ones lie in and near it, than in other parts of heaven. Is not this a strong indication that this astonishing system of worlds beyond worlds innumerable, is not alike extended every way, but confined between two parallel planes, of _immeasureable_, though not _infinite_ extent? Or rather, is not the Milky-Way a vein of a closer texture, running through this part of the material creation? Great things are sometimes best explained by small and small by great. Material substances, such as we daily handle, have been thought composed of impenetrable particles in actual contact: then again it has seemed necessary to suppose them at a distance from each other, and kept in their relative situations by _attraction_ and _repulsion_. Many appearances require that those distances should be very great in proportion to the size of the particles. Hence some, with no small reason, have concluded that matter consists of indivisible points endued with certain powers. Let us compare these smaller portions of it with that great aggregate of matter which is the object of Astronomy; _Light_ will then appear to have as free passage through a piece of glass, as the comets have in the planetary regions; and several other new considerations will arise.

If instead of _descending_ we _ascend_ the scale. If we consider that infinite variety which obtains in those parts of nature with which we are most intimate: how one order of most curiously organized bodies, infinitely diversified in other respects, all agree in being fixed to the earth, and receiving nourishment from thence: how another order have spontaneous motion, and seek their food on different parts of the earth, whilst by gravity they are confined to its surface, but in other respects diversified like the former. How a _third_ float in, and below the surface of, a dense fluid, of equal weight with their bodies, which would soon prove fatal to both the others: And a _fourth_ consisting of a vast variety too, have this property in common, that by a peculiar mechanism of their bodies, they can soar to great heights above the earth, and quickly transport themselves to distant regions in a fluid so rare as to be scarcely sensible to us. But not to pursue this boundless subject any further, I say, when we consider this great variety so obvious on _our_ globe, and ever connected by some degree of uniformity, we shall find sufficient reason to conclude, that the visible creation, consisting of revolving worlds and central suns, even including all those that are beyond the reach of human eye and telescope, is but an inconsiderable part of the whole. Many other and very various orders of things unknown to, and inconceivable by us, may, and probably do exist, in the unlimited regions of space. And all yonder stars innumerable, with their dependencies, may perhaps compose but the leaf of a flower in the Creator’s garden, or a single pillar in the immense building of the Divine Architect.

Here is ample provision made for the all-grasping mind of man!

If it shall please that Almighty Power who hath placed us in a world, wherein we are only permitted “_to look about us and to die_;” should it please him to indulge us with existence throughout that half of eternity which still remains unspent; and to conduct us through the several stages of his works; here is ample provision made for employing every faculty of the human mind, even allowing its powers to be constantly enlarged through an endless repetition of ages. Let us not complain of the vanity of this world, that there is nothing in it capable of satisfying us: happy in those wants, happy in those restless desires, forever in succession to be gratified; happy in a continual approach to the Deity.

I must confess that I am not one of those sanguine spirits who seem to think, that when the withered hand of death hath drawn up the curtain of eternity, almost all distance between the creature and creator, between finite and infinite, will be annihilated. Every enlargement of our faculties, every new happiness conferred upon us, every step we advance towards the perfection of the divinity, will very probably render us more and more sensible of his inexhaustible stores of communicable bliss, and of his inaccessible perfections.

Were we even assured that we shall perish like the flowers of the garden, how careful would a wise man be to preserve a good conscience, during the short period of his existence; because by his very constitution, which he cannot alter, this is his pride and glory, and absolutely necessary to his present happiness; because this would insure to him at the approach of death, the soothing reflection, that he was going to restore, pure and uncorrupted, that drop of divinity within him, to the original ocean from whence it was separated. How much more anxiously careful ought we to be, if we believe, as powerful arguments compel us to believe, that a conduct in this life depending on our own choice, will stamp our characters for ages yet to come. Who can endure the thought of darkening his faculties by an unworthy application of them here on earth, and degrading himself to some inferior rank of being, wherein he may find both his power and inclination to obtain wisdom and exercise virtue, exceedingly diminished? On the other hand, if that humble admiration and gratitude, which sometimes rises in our minds when we contemplate the power, wisdom and goodness of the Deity, constitutes by far the most sublimely happy moments of our lives, and probably will forever continue to do so, there cannot be a stronger incitement to the exercise of virtue and a rational employment of those talents we are entrusted with, than to consider that by these means we shall in a few years be promoted to a more exalted rank amongst the creatures of God, have our understandings greatly enlarged, be enabled to follow truth in all her labyrinths with a higher relish and more facility, and thus lay the foundation of an eternal improvement in knowledge and happiness.

---

[TRANSLATED FROM THE LATIN ORIGINAL.]

_To the illustrious and celebrated Society of Sciences, at
Philadelphia_,

CHRISTIAN MAYER, Astronomer to the most serene Prince, the Elector
Palatine, wisheth prosperity.

I have concluded on due reflection, that the opportunity of writing,
afforded me by the eminent Mr. Ferdinando Farmer, ought the less to be
neglected, as by this means I might make some small return for the
honour which the illustrious Society conferred on me, when they
enrolled me in the list of their members.

I learnt with great pleasure, by a work printed in Philadelphia, and
transmitted to me about three years since, that even there Astronomy
is cultivated. That book, together with my own astronomical papers,
having been destroyed by an unfortunate fire about two years ago, I
have been induced to address something to your illustrious Society,
concerning some of my new discoveries in the heavens.

I occupy a new Observatory at Manheim, accommodated to all
astronomical purposes: nor is it deficient in any of the most valuable
London-made instruments. Among these, the one which principally
excels, is a mural quadrant of brass, of eight feet radius, made by
that celebrated artist Bird, in the year 1776; fitted with an
achromatic telescope, and firmly affixed to a wall, in the meridian;
which I use daily, when the weather permits. I observed, nearly two
years since, that, among the fixed stars, many of them from the first
to the sixth degree of magnitude, other small attendant stars (or
satellites) were distinguishable: some of which, by reason of their
steady and dim light, resemble an order of planets, while others do
not exceed the smallness of the telescopic size. The circumstance
which principally excited my surprize, is, that I found none of those
little attendant stars, a very few only excepted, contained in any
known catalogue; although I could clearly discover that their use, for
the purpose of determining the proper motion of the fixed stars, is
very obvious. For where the difference of right ascension and
declination, of a few seconds at most, is found between the brighter
fixed star and its attendant, the lapse of time could scarcely give
any other variation to the fixed star, than to its satellite: from
what cause soever that variation may arise, whether from the
precession of the equinoxes, the variation in the obliquity of the
ecliptic, the deviation of the instrument, or from the aberration of
light or the nutation, or from any other cause whatever, which may
depend on the mutable state of the atmosphere or the latitude of
places, the fact is evident, that every change of situation, observed,
between the fixed star and its satellite, affords the most certain
proof of its actual motion; whether this be referred to the fixed star
or its satellite.

I knew that Halley, the celebrated English astronomer, was the first,
who, in the year 1719, from an actual comparison of Flamstead’s
observations with those of Ptolemy, respecting some few fixed stars,
Syrius, Arcturus, and Aldebaran, discovered that these stars moved,
with a motion peculiar to themselves: But I knew at the same time,
that in Flamstead’s British Celestial History, so long ago as the year
1690, the name of attendant (or satellite) was assumed by Flamstead;
when that great man had not even thought of the proper motion of the
fixed stars.

Other astronomers, since the time of Halley, so far as they examined
the proper motion of the fixed stars, have followed the Halleian
method, in a comparison of their own observations with those of the
ancients. This method requires long and laborious calculations; and
continues liable to many doubts, on account of its uncertainty, as
well by reason of the inaccurate nature of the instruments, as of the
observations of the ancients. But this is not the case with my new
method; from which, by means of the variation observed between the
satellite and its brighter fixed star, it necessarily results, that
the appropriate motion, either of the one star or the other, is to be
attributed to it. Hence it is, that, within two years past, I have
observed almost two hundred attendants of divers fixed stars; moving
nearly in the same parallel, immediately before or after their
respective fixed stars: and I have communicated many observations of
this kind to the celebrated English astronomer, Nevil Maskelyne, who
assures me they prove highly acceptable to him.

From amongst many of my observations, I transmit to your illustrious
society a few, by way of specimen; the corresponding observations to
which, I find in the Britannic Celestial History of Flamstead; whence
at the same time it is obvious, that observations of this kind are
eminently useful, for the purpose of discovering the proper motion of
such stars.

[The Table, containing the Observations here referred to, will be
found in the second volume of the Society’s Transactions, annexed to
Mr. Mayer’s communication: he then proceeds thus, referring to that
Table.]

The first and second left-hand column of the following Table are
easily understood, from the title. The third column shews the
difference of right ascension, in mean time, between the star and its
satellite: The attendant, preceding the fixed star, is set down in the
first place, in the table; the attendant, following, is placed after
its fixed star. The fourth column notes the difference between the
fixed star and its attendant, as I have observed it at Manheim. The
letter A denotes, that the attendant is to the southward; letter B
more northward. The following columns contain the observations of the
same star, made by Flamstead.

It appears from the whole of the observations, that, of all the stars,
Arcturus is carried with the greatest celerity, by his own motion,
westward; since the same attendant, which in Flamstead’s time, on the
14th of February, 1690, preceded Arcturus 5″ in time, now enters the
meridian 6″ after him. From the diminished difference also, of
declination between Arcturus and his attendant, it is evident, that
Arcturus progresses annually, by his own appropriate motion, nearly 2″
in a circular course, towards the south. From this it clearly results,
that the declination of the attendant, as observed by me, reduced to
the parallel of Greenwich, produces the same altitude of the Greenwich
pole, as that deduced from Flamstead’s observation; but not so, the
declination of Arcturus, observed at the present day, even with the
aberration and nutation corrected.

A similar investigation may be made, with respect to the other fixed
stars and their attendants; and, from the comparison already begun
with other fixed stars, it may be ascertained whether an appropriate
motion is to be attributed to the fixed star or its attendant, or to
both.

All my observations are made in a meridienal plane with a mural
quadrant, at Manheim, in his Serene Highness the Elector Palatine’s
new Observatory, erected for me: its longitude, East from Greenwich,
is nearly 34′ 6″, in time; its latitude, nearly 49° 27′ 50″.

It will give me very great pleasure, if I shall learn that these
observations of mine do not prove unacceptable to your illustrious
society: to whose goodness I most respectfully commend myself; being
ever the very devoted admirer and humble servant of your illustrious
and celebrated Society.

CHRISTIAN MAYER,
Astronomer to his Serene Highness the Elector
Palatine and Duke of Bavaria.

_Manheim, in Germany, April 24, 1778._

---

_Letter from Mr. Rittenhouse to Professor Mayer of Manheim, in Germany._

_Philadelphia, August 20th. 1779._

Sir,

I am directed by the Philosophical Society to acknowledge your letter
of the 24th of April, 1778, and to return you their thanks for
communicating the Observations it contains, wishing you success in
further prosecuting so curious a Discovery. They likewise embrace this
occasion to replace the volume of their Transactions which shared the
fate of your more valuable papers.

This country having been the seat of war, our meetings have been
interrupted for two years past, and the publication of a second volume
thereby prevented; but as the Society is again revived, and we have
materials for the purpose, it will not be much longer delayed.

You will please to accept, by this conveyance, a discourse delivered
some years ago before the Philosophical Society, which I the rather
present you with, because I, therein, gave my opinion that the fixed
stars afforded the most spacious field for the industry of future
Astronomers, and expressed my hopes that the noblest mysteries would
sometime be unfolded in those immensely distant regions.[A40] Your
excellent discovery has proved that passage to be well founded, and I
shall be happy in hearing farther from you on this subject. It is
unnecessary for me to suggest to you a comparison between the many
Observations you have made, in order to determine whether the several
changes observed will agree with any imagined motion of our system.
Those you have communicated seem to favour such a supposition. I am,
Sir, your most obedient and humble servant.

DAVID RITTENHOUSE, _Vice-President_.

-----

Footnote A40:

See page 320 of the foregoing Memoirs.

-----

---

_Some Remarks of Mr. Rittenhouse, on the famous Problem of
Archimedes._[A41]

-----

Footnote A41:

See page 154 of the foregoing Memoirs.

-----

To the Printers of the Pennsylvania Gazette.

_Philadelphia, Oct. 8th. 1767._

Gentlemen,

In your paper, No. 2017, an ingenious gentleman who signs himself T.
T. has favoured the public with remarks upon that celebrated saying of
the famous Syracusean geometrician: “Give me a place to stand on, and
I will move the Earth.” When these remarks appeared, I was engaged in
matters that would not allow me to pay that attention to them, which
they deserved. The justice, however, due to Archimedes, and the
respect I bear for that truly great man’s memory, oblige me now
(though late) to offer my sentiments upon this interesting subject.

I readily agree with your sensible correspondent, as to the conclusion
he has drawn from the principles whereon he seems to have founded his
calculation, without being at the trouble to examine his numbers. All
that I propose is, to place this grand mechanical problem in another
light, wherein it will appear more feasible.

If a ball of earth, weighing 200 pounds, were left at liberty near the
surface of this globe, it would descend, by its own gravity, about 15
feet in one second of time, and about 20 miles in 80 seconds: And if,
as this gentleman supposes, there are about 2000 trillions of such
balls in the whole Earth,—the Earth, by their mutual attractions, in
80 seconds of time; will move toward the ball 1/1736,000,000,000,000
of an inch; and if the same force were to act continually for 105
years, it would move about one inch. Therefore, the force wherewith a
man acts, when he lifts a weight of 200 pounds, if applied without
intermission for the space of 105 years, is sufficient, without any
machinery, to move the Earth one inch in that time;[A42] and it must,
from the velocity received by that force alone, continue for ever
after to move at the rate of one inch in about 50 years.

A MECHANIC.

-----

Footnote A42:

Mr. T. T. proceeding on a different supposition, has computed
twenty-seven billions of years necessary for that purpose.

-----

---

_Letter from Mr. Rittenhouse, to the Rev. Mr. Barton._

_Norriton, July 20th. 1768._

Dear Brother,

In Hall and Sellers’ paper of last Thursday, we have some curious
remarks on an Essay for finding the Longitude, lately published in the
Pennsylvania Chronicle, and which I had before seen in the London
papers.

The first remark is no doubt just, and is perhaps the only one made,
which Mr. Wood’s essay gave just occasion for; how he could commit
such a mistake, is not easy to conceive. But the remarker immediately
charges him with another: for he tells us, that he (Mr. Wood I
suppose) says, that Mr. Harrison’s Machines were finished about
Christmas 1765; whereas his father (whether Wood’s father or
Harrison’s, is not clear,) made three, which the remarker saw in
motion about 18 years since. He then proceeds to assure us, (by the
spirit of prophecy I presume, at least I cannot conceive how he could
come by this piece of knowledge in a natural way,) that neither the
father or his son will ever be able to finish their machines.

A machine, says the remarker, to measure the mean motion, will be far
preferable to any other method yet proposed; and immediately
afterwards he confesses, he cannot conceive that a true meridian can
be found at sea, to several minutes. Now this “uncertain error” must
certainly affect any other machine for that purpose, as well as Wood’s
Sand-Glass, and exceed the error occasioned by turning the glass
somewhat quicker at one time than another. Besides, it would not be
easy to shew, why a machine to measure the Earth’s mean motion on its
axis, with respect to the Sun, will be preferable to one that will
measure the Earth’s true motion on its axis, with respect to the fixed
Stars.

I would not be thought to recommend Wood’s project. He himself takes
notice of two disadvantages attending it, viz. the wearing of the
orifice through which the sand passes, and the sand itself becoming
polished in time, so as to run more freely; to which if we add, that
perhaps it may be greatly affected by heat and cold, there seems to be
but little probability of its usefulness. Nor do I see how it can even
have the merit of being new: for the scheme itself, with all the
remarker’s objections that have any weight in them, must readily occur
to every person that thinks at all on the subject. I shall only
observe, that it appears doubtful to me, whether the remarker does not
equally deserve the censure he so freely bestows on Mr. Woods—“His
works are full of errors, and his writings of contradictions.”

* * * * * * * * * *

I remain your affectionate brother.

DAVID RITTENHOUSE.

---

_Dr. Rittenhouse’s Chronometer._

The construction of this Time-piece is thus described by Mr. Henry
Voight, chief coiner in the Mint, heretofore an eminent clock and
watch maker in Philadelphia; an artist of great ingenuity, and well
known for the excellence of his workmanship. The description is
given in Mr. Voight’s own words.

“The Clock which Dr. Rittenhouse made use of in his Observatory was a construction of his own. It had but three wheels in its movement, of high numbers. Only one pinion, without a wheel, driven by the main wheel; whose axis goes through the front plate, that carried the dial-work; and this wheel[A43] has a perpetual rochet.[A44] The seconds are eccentric, as in the common clocks.

-----

Footnote A43:

“The main-wheel, which is fixed on the barrel on which the cat-gut
runs.” _Mr. Voight._

Footnote A44:

“A perpetual rochet is a spring lying between the main-wheel, and a
plate which is so high in diameter as to be nearly of a height with
the bottom of the main-wheel teeth, and is cut with fine teeth all
round, in the shape of a fine saw. A click on an axis is fixed between
the two frame-plates, with a weak spring that forces this click into
the fine saw-teeth, which keeps the plate from moving backwards when
the clock is winding up. This fine rochet-wheel is fixed on the
barrel-arbour or axis, the same as the main-wheel. The barrel-rochet
comes close against the plate of the fine rocket, which has a click
screwed on the front, corresponding with the barrel-rochet, and a
spring above that rochet’s click, which forces that click into the
barrel-rochet’s teeth: it is this that makes the clattering noise,
which is heard when a clock is winding up: There is a middling strong
spring placed between two arms of the cross of the main-wheel, bent
like the space of the two arms between which it acts; and this spring
is as broad as the thickness of the cross-arms. One end of that spring
is fastened to the inside of the fine rochet-plate: the other end lies
on the other cross-arm, and acts on that like a gun-lock mainspring on
the cock-tumbler. When the clock or time is set a going, and the
maintaining power or weight of the fusee or barrel, this power will
raise that spring so far as to resist the maintaining power, and
becomes stationary as long as the time-piece is going; and when it is
wound up, this spring in the main-wheel cross will expand itself,
press on the cross-arm, and force that wheel forward, with nearly the
same power as the maintaining power would give: the click for the
fine-teethed rochet falls into one of those fine teeth, and keeps that
rochet steady, without having the least motion, as long as the
winding-up of the clock continues; and by this means a time-piece can
lose no time in winding up: hence it is called a perpetual rochet;
which requires the most accurate workmanship, in its construction.”
_Mr. Voight._

-----

“The pallet-wheel moves outside of the back-plate, and the pallets are fastened to the rod of the pendulum, which has double suspending springs fixed in a cross-bar, to which the rod is rivetted in the middle. These springs are suspended as in common; but they are not so long as in general, and have only one-and-an-half inch free action, which keeps the pendulum very steady in its vibrations.

“On the rod of the pendulum there is fixed a glass tube, of the thickness of a strong thermometer-tube, and is in the whole as long as the rod: but it is bent, about one-third upwards; like a barometer, but longer; and upon that end, on the top, the tube is as wide again as it is below, for about one-and-an-half inch in length: the other two-thirds of the length is filled with spirits of wine; and at this end, the tube is hermetically sealed. The shorter part is filled with mercury, so high as to fill the widest part of it, about half an inch, and is not sealed but remains open. The bend is close together, and there is no more space between the tubes than three-eighths of an inch.

“This tube is fastened to the pendulum-rod with common sewing-thread, and rests upon two pins fixed in the bob of the pendulum, as high up as possible. The bob has no slide, but is immoveable; and the regulation of the pendulum is performed by adding to, or diminishing the mercury, in the part where the tube is widest.”

In addition to the foregoing description of the mechanism of this
Time-piece, obligingly furnished to the Writer of these Memoirs by
Mr. Voight, he has been likewise favoured by Robert Patterson, Esq.
director of the mint, with the following account of the same
extremely accurate instrument, which will greatly assist the reader
in understanding the principles on which it is constructed.

“In the Astronomical Clock made by Dr. Rittenhouse, and now in the Hall of the Philosophical Society, I do not know,” says Mr. Patterson, “that there is any thing peculiar, which requires mentioning, except the pendulum; especially the apparatus for counteracting the effects of change of temperature.

“For this purpose, there is fastened on the pendulum-rod (which is of iron or steel) a glass tube of about thirty-six inches long; bent in the middle into two parallel branches, at the distance of about an inch from each other; the bend being placed downwards, immediately above the bob of the pendulum. The tube is open at one end, and close at the other: the arm which is close at top is filled, within about two inches of the lower end or bend, with alcohol, and the rest of the tube, within about one half of an inch of the upper extremity or open end, with mercury; a few inches of the tube, at this extremity, being about twice the width of the rest of the tube.

“Now, when the heat of the air encreases, it will expand the pendulum-rod; and would thus lower the centre of oscillation, and cause the clock to go slower: but this effect is completely counteracted, by the expansion of the alcohol chiefly, and of the mercury in part; which equally raises the centre of oscillation; and thus preserves an equable motion in all the variable temperatures of the atmosphere.”

---

_Description of an Hygrometer; first contrived and used by Dr.
Rittenhouse, about the year 1782._[A45]

-----

Footnote A45:

This description is drawn up from two separate accounts of the
instrument, with which the Writer of these Memoirs was obligingly
furnished, in writing, by Robert Patterson and the late David
Rittenhouse Waters, Esquires, of Philadelphia. Mr. Patterson mentions,
that he recollects his having seen the Hygrometer so described, in Dr.
Rittenhouse’s Observatory, about thirty years ago.

-----

The essential part of this Hygrometer consists of two very thin strips of wood, about a foot long and half an inch broad, glued together, in such a manner that the grain or fibres of the one shall be at right angles with the other; so that when this compound strip was placed in erect position, the grain of one of the pieces of wood would have a vertical, and that of the other an horizontal position. One end of this simply constructed instrument is to be made fast to a wall, or plane board, with the edge outward, and the other end is to be at liberty to move.

Then, as moisture has little or no effect on the length of a piece of wood, or in the direction of its fibres, but a very sensible one on its breadth, or transverse direction, especially when thin, it follows, that on any increase of moisture in the air, this Hygrometer becomes bent into a curve, convex on the side of the transverse fibres; and _vice versâ_. The degrees, from the greatest dryness to the greatest moisture, are to be marked on a curve drawn on the board or wall, described by the motion of the free end of the Hygrometer; and an index, attached to the moving end of it, will point out, on this graduated arch, the existing state of the atmosphere at the moment, in relation to its condition of moisture or dryness: The relative degree of either, on the smallest change from the one to the other, will be indicated with much precision; and probably, with much more uniformity and truth, in the results of long-continued observations, than can be attained to by the use of Hygrometers constructed of metal, or any other substance than wood.[A46]

-----

Footnote A46:

The second volume of the Transactions of the American Philosophical
Society contains a letter, written on the 13th of November, 1780, by
Dr. Benjamin Franklin, then in France, to Mr. Nairne, of London: but
it was not communicated to the Society, until January, 1786.

In that letter, Dr. Franklin suggests to Mr. Nairne (an eminent
optician, and mathematical instrument maker,) the idea of an
Hygrometer made of wood; in preference to metalline instruments, for
the purpose of discovering “the different degrees of humidity in the
air of different countries;”—an idea which occurred to the Doctor, in
consequence of a casual circumstance, mentioned in his letter.

Dr. Franklin supposed “a quick sensibility of the instrument, to be
rather a disadvantage” to it; “since,” says he, “to draw the desired
conclusions from it, a constant and frequent observation day and
night, in each country—when the design is, to discover the different
degrees of humidity in the air of different countries—will be
necessary for a year or years, and the mean of each different set of
observations is to be found and determined.”—“For these reasons,”
continues the Doctor, “I apprehend that a substance which, though
capable of being distended by moisture and contracted by dryness, is
so slow in receiving and parting with its humidity that the frequent
changes in the atmosphere affect it sensibly, and which therefore
should, gradually, take nearly the medium of all those changes and
preserve it constantly, would be the most proper substance, of which
to make an Hygrometer:”—and he believes _good mahogany wood_ to be
that substance. In the concluding part of this letter, Dr. Franklin
says to his correspondent: “I would beg leave to recommend to you—that
you would take a number of pieces of the closest and finest grained
mahogany that you can meet with; plane them to the thinness of about a
line, and the width of about two inches across the grain, and fix each
of the pieces in some instrument that you can contrive, which will
permit them to contract and dilate, and will shew, in sensible
degrees, by a moveable hand upon a marked scale, the otherwise less
sensible quantities of such contraction and dilatation.”

Hence it appears, that Franklin and Rittenhouse conceived an idea of
the same kind, nearly at the same time: but that the latter carried
his invention into practice, three or four years before the theory of
the former, founded on similar principles, had been announced to the
American public, or, as it is believed, was made known to any other
person than Mr. Nairne. W. B.

-----

_Astronomical Observations, made in the years 1776, 1777 and 1778, at
Philadelphia, by the Rev. Dr. W. Smith, and David Rittenhouse, John
Lukens, and Owen Biddle, Esquires: copied from a manuscript account of
those Observations, drawn up by Dr. Smith; never before published._

ASTRONOMICAL OBSERVATIONS, 1776.

This year exhibiting little else but scenes of confusion and distress amidst the calamities of an unhappy war, scarce any attention was paid, by the members of the American Philosophical Society, to astronomical or any other literary subjects. It was agreed, however, by Mr. Rittenhouse, Mr. Lukens and myself, to look out whether Mercury would touch the Sun’s disc the 2d of November this year; as a very small difference of latitude from what the Tables give, would have carried the planet clear of the Sun: but, from our observation of the transit of this planet, in 1769, we had reason to expect it would pass further on the Sun, than Halley’s Catalogue gives it.

The following were the observations made, viz.

Nov. 2d, 1776. I got ready the two f. reflector with the largest object-glass, and shortest eye-tube, magnifying about 95 times.

At 4^h per clock—No appearance of the planet on the Sun, and did not expect it until about half an hour past 4; but as Mr. Lukens and Mr. Rittenhouse had not yet come to me in the college, I sent to hasten them.

At 4^h 5′ per clock—took my eye from the tube to adjust it, and fix the smoked glass, to give clearer vision, the atmosphere being hazy. Having fixed the smoked glass in the proper place, so as to prevent its sliding or falling with its own weight, and before I had applied my eye to the telescope again, Mr. Rittenhouse came in; and I desired him to see if the focus and dark glass were all suitable to his eye, as they were to mine. I had been about 4′ employed in this adjustment.

At 4^h 9′, Mr. Rittenhouse having put his eye to the tube, immediately called out, that he saw the planet on the Sun.

At 4^h 10′ per clock, we judged ☿ had entered one-third of his diameter on the Sun.

At 4^h 17′, we clearly noted the internal contact of the limbs.

At 4^h 45′, we judged the least distance of the nearest limbs to be rather more than one diameter of ☿; or that the distance of the limbs was 10″. We-did not apply the micrometer to make any measures; as we presumed that we could judge the distance as accurately by the eye, as it could be measured; on account of the haziness of the atmosphere and the small altitude of the Sun. We kept viewing the planet till sun-set, the distance of the limbs continuing so nearly the same, that we could scarce perceive any diminution thereof; though we were sure also, that it did increase above 10″.[A47]

-----

Footnote A47:

In a table (in the 2d vol. of Lalande’s _Astronomie_,) entitled,
“_Passages de Mercure sur le Soleil, calculés pour trois siècles par
les nouvelles Tables_,” the transit of that planet, above referred to,
is thus set down by Lalande, at Paris; viz.

Year. Conjunct. Mean Geocentric Mid. Mean Semi-dura. Short. Time. Long. Time dist. 1776. Nov. 2. 9^h10′7″. 7.11°3′36″. 9^h49′53″. 0^h36′42″. 15′43″.A

W. B.

-----

The following were the Observations made for ascertaining the Going of the Clock, by WILLIAM SMITH.