[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.]