Chapter 27

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[TRANSLATED FROM THE LATIN ORIGINAL.]To the illustrious and celebrated Society of Sciences, at Philadelphia,

[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, NevilMaskelyne, 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 whetheran 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 ElectorPalatine and Duke of Bavaria.Manheim, in Germany, April 24, 1778.

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, NevilMaskelyne, 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 whetheran 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 ElectorPalatine and Duke of Bavaria.

Christian Mayer,

Astronomer to his Serene Highness the Elector

Palatine and Duke of Bavaria.

Manheim, in Germany, April 24, 1778.

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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 thatthe 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.

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 thatthe 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.

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

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.

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.

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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 atone 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.

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 atone 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.

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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.

“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.”

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

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; andvice 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]

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 4hper 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 4h5′ 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 4h9′, Mr. Rittenhouse having put his eye to the tube, immediately called out, that he saw the planet on the Sun.

At 4h10′ per clock, we judged ☿ had entered one-third of his diameter on the Sun.

At 4h17′, we clearly noted the internal contact of the limbs.

At 4h45′, 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]

The following were the Observations made for ascertaining the Going of the Clock, byWilliam Smith.

Equal Altitudes.d h′ ″h ′ \″Nov.3 914 92 37 12{☉ on Merid. per clock{h ′ ″15 442 35 35or mean noon11 55 40Equat. Correspond. Alt.+ 14.4Correct Noon per Clock11 55 54.44 932 4820 56{Mean Noon, or ☉ on{11 56 5334 3319 13Merid. per. Clock36 1417 31Equat. of equal+ 13.837 2016 23Altitudes14 3940 542 12 53Correct Noon per Clock11 57 6.87 851 99 29{Mean Noon{12 0 1952 378 0per ClockEquat Eq.Alt. + 1254 13 6 3712 0 19Cor. Noon12 0 31per Clock

Per Meridian Mark.

dh ′ ″8☉West Limb on Merid.12 0 36East Limb on do.12 2 52—-——Centre12 1 44Correct Noon per Clock.

Applied to Going of Clock.

Nov. 3d, at Noon′ ″{Clock slower than ☉4 5.6Daily gaining of the Clock overmeanorequaltime.☉ faster than mean time16 11Clock faster than m. time12 5.44th,{Clock slower than ☉2 53.2′ ″☉ faster than mean time16 9From 3d to 4th1 10.4Clock faster than m. time13 15.87th,{Clock faster than ☉0 31From 4th mean to 7 that a mean per day{1 5.1☉ faster than mean time16 00Clock faster than m. time16 318th,{Clock faster than ☉1 44☉ faster than mean time15 56From 7th to 8th1 9Clock faster than m. time17 40Thus the Clock gains at a mean, per day, 1′ 8″.

Whence, Nov. 2d, at noon, the Clock was 10′ 57″ faster than mean time, gaining 68″ per day; and 4h17′ gains 12″, wherefore at the internal contact, the Clock was 11′ 9″ faster than mean time.

Whence the contact was at 4h5′ 51″ mean time; or 4h21′ 2″ apparent time.

Eclipse of the Sun, January 9th, 1777.

The Gregorian Reflector, with the magnifying power of 95, was made use of for this Observation; which, as well as the Observationof the Transit of Mercury, was made in the College-Library, to which the Telescope belongs.

While Mr. Rittenhouse was endeavouring to adjust the two-f. reflector belonging to the Library of the city of Philadelphia, made by Short, and which had been borrowed on this occasion, I observed with the greatest certainty the first contact of ☾’s limb with the ☉, which was shining very bright, and the telescope in the best order, viz. at 8h57′ 27″ per clock.

The same was visible, in about 3″ more, to Mr. Lukens, with the equal altitude instrument, magnifying about 25 times.

Mr. Rittenhouse had not got the other reflector ready to observe the beginning of the eclipse: but the end was observed by both of us to the same instant, viz. at 11h48′ 50″ per clock.

The clock, at noon, was 23″ slower than mean time, whence

Beginning of the Eclipse8h49′ 55″{Apparent time.End of the same11 41 15

N.B. The clock stopped once during the Observation, owing, it was supposed, to the cold weather; but was oiled a little, and set a going again by a stop-watch that beats seconds, and which was set with the clock at the beginning of the eclipse: so that she lost no time. She was examined at noon, and found as above by the meridian mark. But this mark itself, having been lately shaken with the stormy weather, is to be re-examined, and also equal altitudes taken the following days.

The annexed micrometer measures were taken for determining the quantity of the eclipse, chiefly by Mr. Rittenhouse. More would have been taken, but the Sun was hid under clouds for about an hour after the middle of the eclipse, and broke out again a little before the end.

Micrometer Measures.

h′″inches.tenths.500ths.9150226{distances of the cusps.31031½101751114{enlightened parts remaining.220112311370176{38461521distances of the cusps.42261218

Continuation of the Observations for adjusting the Clock.

Jan. 11th.☉’sW. limb on Merid.{[A48]E. limb on do.Centre on do.

Whence clock faster than mean time 0 1′ 46″ per merid. mark.

Equal Altitudes.h′″20th.937205949{391586Mean noon per clock 12 18 3440412562621st.W. limb on Merid.12203E. limb on do.2222Centre on do.122112.5Eq. Alt.22d.9141033110Mean noon per clock 12 23 50

Eclipse of the Sun, June 24, 1778: Observed by D. Rittenhouse, John Lukens, Owen Biddle, and William Smith, at the College of Philadelphia.

The morning being very cloudy, the beginning of the eclipse was not seen.

At 10h7′ 40″ per clock, the following micrometer-measure of the enlightened parts was taken, while the Sun appeared for a few minutes between clouds, viz. 1in.9-10ths.13-500ths.= 16′ 23″.

11h6′ 57″ per clock end of eclipse distinctly seen, the Sun having shone clearly for several minutes, the clouds now wholly dispersing, and the remainder of the day continuing clear.

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