parallax in any star amounting to a single second, and this was a quantity so difficult to answer for, that the discovery of any parallax seemed almost hopeless. A satisfactory solution of this much vexed problem was reserved for Bessel.

All the stars have a general motion of translation, which tends ultimately to mix the individuals of the different constellations, but none that we know of moves so rapidly as 61 Cygni. This is a star of the fifth or sixth magnitude, barely visi ble to the naked eye. Seen through a telescope, this star is found to consist of two, of nearly equal brightness, distant from each other about 16" of arc, and this distance has remained nearly the same for at least fifty years, but is slowly increasing. Meanwhile they have shifted their local situation in the heavens in this interval of time, through 263", the annual proper motion of each star being 5".1, by which quantity this system is every year carried bodily along in some unknown path. On account of its great proper motion, this star has long been reckoned to be nearer to us than any other, for an object seems to move more quickly the nearer we are to it. This circumstance induced MM. Arago and Mathieu to endeavor to determine its annual parallax. They found that this could not exceed a half second, but how much less, remained undetermined. This discovery was reserved for Bessel. To understand the principle of the method employed, imagine two stars situated nearly on the same line passing though the earth, but at very unequal distances from us; it is obvious, that any motion of the earth must produce different displacements of the two stars on the surface of the heavens. If we measure carefully with micrometers adapted to the purpose, their apparent situation with respect to each other at different times of the year, we should find a periodical change both in the direction of the line joining them, and in the distance between them. Thus it is not the absolute parallax of either, but the difference of their parallaxes, which is measured by this method. This

Frederic William Bessel, was born at Minden, in Germany, July 22, 1784, and at the age of fifteen years entered one of the first com mercial houses of Bremen. The maritime intercourse of that place with foreign countries, excited in him an inclination for geography, and afterwards for the science of navigation, and induced him to attempt the acquisition of mathematical knowledge from books. He soon passed to astronomy, and as his days were otherwise occupied, he devoted his nights to these labors. An astronomical work which he wrote, procured him the acquaintance of Dr. Olbers, (a resident of Bremen,) who from that time became his adviser. In 1806, he joined Scröter at Lilienthal, with recommendations from Olbers, and was employed for four years as inspector of the instruments belonging to the University of Göttingen. From thence he was invited to Königsberg, where he built in 1812 -13, the observatory, which is a monument of the scientific enterprise of the north of Germany, since it was erected when Prussia was almost exhausted by war, and Königsberg was situated on the great theater of Napoleon's operations against Russia. This observatory was, till 1819, provided with English instruments, when the ministry supplied it with the means of procuring new ones, made by Reichenbach, of the best workmanship. No one knows better how to use his instruments than Bessel, being considered by many the best astronomical observer of the present age. This is the man who has undertaken to settle the long-mooted question of parallax of the stars.

mode of observation has the advantage, that the two stars will be equally affected by refraction, errors of graduation, aberration, etc. Let us hear the account of this discovery in Bessel's own words. "In September, 1834, I began the comparison of the star 61 Cygni with my great Fraunhofer heliometer," by measuring its distance from two small stars of the eleventh magnitude, of which one precedes and the other is to the northward. But I soon perceived that the atmosphere was seldom sufficiently favorable to allow of the observation of stars so small, and for two or three years afterwards, my time was constantly occupied with other enquiries. In 1837, I selected among the small stars which surround that double star, two between the ninth and tenth magnitudes; of which, one (a) is nearly perpendicular to the line of direction of the double star; the other (b) nearly in the same direction. I have measured with the heliometer the distance of these stars from the point midway between the two stars of 61 Cygni. The distance of (a) is 461", of (b) 706". I have found the difference of annual parallax of 61 and (a) 0.3584; of 61 and (b) 0.3289. The mean error of the parallax deduced is not of its entire value. Assuming the parallax of (a) and (b) to be equal, its most probable value is 0.3483; whence the distance of the star 61 Cygni is five hundred and ninety two thousand and two hundred times the mean distance of the earth from the sun. Light, which requires about eight

* This is a telescope with its object glass divided in the middle, and the two parts capable of sliding upon each other, as also of being revolved about the axis of the tube. It gives two images of an object, whose distance is proportioned to the separation of the two parts of the lens. It is therefore a species of micrometer. It was originally employed for measuring the sun's diameter-hence its name, heliometer.

minutes to come from the sun to the earth, would employ nine and a quarter years in traversing this enormous distance. The orbit described by these stars about each other, will therefore be about two and a half times that of Uranus, and the time of their revolution about each other is more than five hundred and forty years. Hence it is computed, that the sum of the masses of both stars is less than half the sun's mass.

In 1841, the Royal Astronomical Society of London, presented their gold medal to M. Bessel for this discovery. From the address of the President, Sir John Herschel, we extract the following remarks. "It is an immense aecession to our knowledge, to have measured the distance of a single fixed star. To accomplish this, has been the object of every astronomer's highest aspirations ever since sidereal astronomy acquired any degree of precision. But hitherto it has been an object, which, like the fleeting fires that dazzle and mislead the benighted wanderer, has seemed to suffer the semblance of an approach only to elude his seizure when apparently just within his grasp, continually hovering just beyond the limits of his distinct apprehension, and so leading him on in hopeless, endless, and exhausting pursuit. Gentlemen, I congratulate you and myself, that we have lived to see the great and hitherto impassa. ble barrier to our excursions into the sidereal universe-that barrier against which we have chafed so long and so vainly, (æstuantes angusto limite mundi,) thus fairly overleaped. It is the greatest and most glorious triumph which practical astronomy has ever witnessed. Perhaps I ought not to speak so strongly-perhaps I should hold some reserve in favor of the bare possibility that it may be all an illu sion, and that further researches, as they have repeatedly before, so

may now fail to substantiate this noble result. But I confess myself unequal to such prudence under such excitement. Let us rather accept the joyful omens of the time, and trust that, as the barrier has begun to yield, it will soon be effectually prostrated. Such results are among the fairest flowers of civilization. They justify the vast expenditure of time and talent which have led up to them; they justify the language which men of science hold, or ought to hold, when they appeal to the governments of their respective countries for the liberal devotion of the national means in furtherance of the great objects they propose to accomplish. They enable them not only to hold out, but to redeem, their promises, when they profess themselves productive laborers in a higher and richer field than that of mere material and physical advantages. It is then when they become (if I may venture on such a figure without irreverence) the messengers from heaven to earth of such stupendous announcements, as must strike every one who hears them with almost awful admiration, that they may claim to be listened to when they repeat in every variety of urgent instance, that these are not the last of such announcements which they shall have to communicate-that there are yet behind, to search out and to declare, not only secrets of nature which shall increase the wealth or power of man, but truths which shall ennoble the age and the country in which they are divulged, and by dilating the intellect, react on the moral character of mankind. Such truths are things quite as worthy of struggles and sacrifices as many of the objects for which nations contend, and exhaust their physical and moral energies and resources. They are gems of real and durable glory in the diadems of princes, and conquests, which, while they leave no

tears behind them, continue forever unalienable."

The apparent motion of five seconds annually, which this star has, seems to us to be extremely small, yet its absolute motion is more than a thousand millions of miles annually, or forty four miles per second, which is more than double the velocity of the earth in its orbit-and this is what we call a fixed star.

The two preceding sketches of astronomical history illustrate the importance of public observatories. We should never have learned the existence of Ceres nor the distance of a single fixed star, without systematic observations with large and accurate instruments. We propose therefore to give some account of a modern astronomical observatory, and to find a model of its kind, we must take our readers to Russia. The history of the progress of science in Russia is nearly as extraordinary as that of free institutions in this country. A century ago, Russia was scarce emerged from the depths of barbarism. One of the last acts of that wonderful man, Peter the Great, was the erection of an academy of sciences at St. Petersburg, in 1725, and the establishment of an observatory, which was presented with costly instruments by Catherine II. No great advance was however made in Russian astronomy, until the accession of the late emperor Alexander. Under him, the observatories at Dorpat and Abo were founded and furnished with instruments, which placed them on a level with the richest establishments of Europe. For Dorpat was procured the great refractor of Fraunhofer, the masterpiece of that incomparable artist. A third observatory was erected at Nicolajef on the Black Sea. Under the reign of Nicholas, astronomy has been patronized with renewed zeal. The resources of Dorpat were augmented. A new ob

servatory has been established at Helsingfors, another at Cazan, and another at Moscow, so that during one generation, more has been done by the Russian government for astronomy, than by any other state during an equal period in the whole history of the science. For several years the idea had been entertained of establishing a central observatory at St. Petersburg; and its erection was decreed in 1833. This plan contemplated,

1. Regular and complete observations, aiming at the perfection of astronomy as a science.

2. Corresponding observations in reference to the geographical enterprises undertaken in the empire

and abroad.

3. The perfection of practical astronomy in its application to geography and navigation.

The observatory was completed in 1838. It is located on the hill of Pulkova, about eleven miles south of St. Petersburg. It consists of two parts; the observatory proper, constituting the main body of the building, and the wings, designed as dwellings for the observers. The whole together, presents a front of eight hundred and forty English feet from east to west. The observatory proper, forms a cross two hundred and twenty feet from east to west, and one hundred and, seventy feet from north to south.

The cut prefixed to this article rep resents the ground plan and elevation of the observatory proper. The principal front is towards the north, where is also the main entrance. By this door we enter an ante-room, a, which leads to the central hall of the observatory, A. This room is a square, fifty five feet on a side, truncated at the angles. Within are seen eight columns upon which rests the great dome. This room has a vaulted ceiling, and is lighted by four windows in the truncated angles. The inner circular area

serves for the reception of com. pany, and has in the middle a large pillar connected directly with the foundations, in a niche of which the main clock of the observatory is placed. The open side of the niche is closed by three plates of glass separated from each other, and thus the temperature of the clock can not vary sensibly in twenty four hours. With this main clock, all the other clocks used in the different rooms of the observa. tory are compared by chronometers. The rooms, a and A, are both warmed by pipes proceeding from under the entrance. The chamber, b, can also be raised in the same way to a high temperature. It has besides, a free communication with the open air, so that it may be suddenly cooled in winter. This contrivance is designed for testing the compensation of clocks and chronometers, before they are erected in their places. c is the stairs which lead to the great dome. It conducts first to a hall over the vault, where is a convenient retreat for the ob server who is employed with the instruments in the dome. The dome, which rests upon an iron railway, has a diameter of thirty two feet, and a height of thirty feet on the inside, twelve of which belong to the surrounding wall, and eighteen to the revolving part. On the south is the office of the direc tor, d, and then the room, B, where is the transit instrument in the prime vertical. East and west from A, are the halls, C and C', for the meridian instruments. Each hall is fifty two feet by thirty five, and can accommodate two instruments. There are therefore four meridian openings, one of which is however not used at present. The height of the hall is twenty three feet. The halls, C, C', and B, are constructed entirely of wood, to obtain a more constant equilibrium between the internal and external temperatures. Next to the halls, C and C', are

two wings of solid masonry, having revolving domes, each twenty feet diameter and twenty high. Under the vaults supporting these instruments are two rooms, D and D', one of which is used for lectures on practical astronomy, the other for the library. e, f, g, h, are four rooms for the accommodation of observers. The observatory cost over a million of rubles,* exclusive of the land given by the emperor, amounting to fifty two acres.

Instruments. In the summer of 1834, Prof. Struve was sent abroad for the purchase of instruments, which were made chiefly at Munich and Hamburg.

1. Great refractor made by Merz and Mahler, at the Optic Institute, Munich. Erected under the great central dome. Clear aperture of the object glass 14.93 inches, focus 22 feet. The instrument rests upon a block of hewn granite, is mounted equatorially and furnished with clock work, so that when once directed upon a star, the star remains as if stationary in the center of the field of view. The telescope has a variety of micrometers, with magnifying powers from 138 to 1822. The finder has an aperture of three inches, and a focal length of forty five inches. This instrument is employed in measurements of double stars, particularly those in which a proper motion is known or suspected. It is the largest refracting telescope hitherto constructed. Cost seventy six thousand rubles.

2. The heliometer, executed at the Optic Institute, Munich, by Merz and Mahler. Erected in the east dome. Aperture of the object glass 7.5 inches; focus 10 feet. The instrument is constructed mainly like the famous Königsberg heli

*A silver ruble is equal to seventy four cents; a paper ruble, which is supposed to be intended here, is worth twenty

cents.

ometer, with some peculiarities. Rests on a block of hewn granite.

3. In the west dome is a comet seeker from Munich, of 3.8 inches aperture, equatorially mounted.

The

4. Transit instrument in the prime vertical, by the Repsolds of Hamburg. Erected in the south hall, B. Clear aperture of the object glass 6.25 inches; focus 7 feet 7 inches. Magnifying power used in the observations, 262. In the focus of the telescope are stretched fifteen vertical lines and two horizontal ones. The object of the instrument is to determine the meridian zenith distance of such stars as culminate a little south of the zenith. transit of a star over seven of the vertical lines is observed; the instrument is reversed, and the transit is continued over the same lines in the inverse order. After a time the star approaches the west vertical, when the same observation is repeated. From such observations, the zenith distance of the star when on the meridian is easily computed; and it is considered the most accu rate method yet employed for detecting small changes of declination.

5. Meridian circle by the Repsolds, in the east hall, C'. Telescope 6 feet, 11.2 inches focus; 5.8 inches aperture. Magnifying power employed, 246. The object glass and eye glass may be made to change places in the tube to eliminate the effect of flexure. Has two circles, each four feet diame ter, graduated to 2. Each circle is furnished with four microscopes. This instrument is designed to furnish a catalogue of about thirteen thousand stars, down to the severth magnitude inclusive, comprehended between the north pole and 15° south declination.

6. Meridian transit instrument, by Ertel of Munich; placed in the west hall, C. Aperture of the object glass 5.8 inches; focus 8 feet, 6 inches. Magnifying power in common use, 292.