$5. THE DOUBLE-STARS MEASURED AT HARTWELL BY

CAPTAIN SMYTH.

In my Cycle of Celestial Objects (vol. i. pp. 285-304), I have given a condensed view of the highly interesting department of Compound Stars, which work can be referred to by many: but as it will not be accessible to all who may honour these pages, a prefatory word or two may be considered necessary towards their comprehending the glimpse which will be afforded of the wondrous works of the OMNIPOTENT FLAT.

Then speak thy humblest thanks; that thus 'tis giv'n

To thee (a worm, a mite, an atom! plac'd

On this small Earthly Ball, to th'universe
Like dust of balance, or the bucket's drop,)

To read, to trace, to know His glorious works.

It will be recollected that a dark and silent void space extends above, below, and around our system, which has been successfully pierced by the force of genius and art: this, indeed, is the triumph of Man's intellect, for the abyss is so inconceivably vast as absolutely to stun contemplation, the distance to the nearest star (a Centauri) being estimated at not less than twenty-one million millions of miles. But the void which thus awfully separates us from the sidereal heavens is known to expand towards other bodies in such a ratio, that the distance of a Centauri is comparatively small; and imagination is confounded, even with the facts demonstrated. Among the assemblage of stars which deck the heavens, in numbers so vast as to be absolutely infinite, many individuals appear as single objects to the naked eye, which are found really to consist of two, or more, under some of the finest and most delicate forms of vision conceivable. Most of these, from their enormous distance, appear to be so close to one another, that it requires telescopes of great perfection to separate them. The practical astronomy of these

elegant objects originated in the unprecedented labours of the elder Herschel at Slough, and constituted one of his greatest bequests to science. When he commenced the inquiry, the circumstance of a star being double was readily accounted for, by supposing one star to be situated at an immense distance beyond the other; and therefore it was presumed to be only optically double, or the two components so nearly in a line with our eye as scarcely to subtend a perceptible angle, yet without any real proximity between them. It was owing to his sagacious perseverance, especially as regarded the observations of that beautiful double-star Castor, on an interval of twenty-five years (1778 to 1803), that the relative places of the components were ascertained to vary; and that the changes detected had no relation to the orbital position of the Earth. In the course of the scrutiny which he prosecuted, it was proved that in various cases the stars were physically binary, and that the companion must actually revolve about its primary. Thus the wonderful truth opened to view, that two suns, each self-luminous and probably with an attendant train of planets, were gyrating round their common centre of gravity under the same dynamical laws which govern the solar system: that is, not precisely like our planets round one great luminary, but where each constituent with its accompanying orbs revolves around an intermediate point, intermediate point, or fixed centre. This is a great fact; and one which, in all probability, Newton himself never contemplated.

But in mentioning the persevering sagacity of Sir William Herschel, I must not forget the palmam qui meruit ferat axiom: for the merit of having first given a method of determining, from observation, the form of the orbit of a binary star, certainly belongs to M. Savary. It is true that Sir John Herschel, struck with the idea that gravitation must be the law of motion in those distant regions, recommended constant observation upon Ursa Majoris so far back as 1825; but Savary was the first in the field with a set of elements for the same from calculation. These he published in 1830, shewing that the comes moved in an ellipse precisely like the planets of our own system, though of a more varied ex-centricity.

The field is peculiarly attractive to the amateur or extra-meridian astronomer, and was therefore invaded from my station at Bedford. Having thus become deeply interested in stellar physics, and therefore anxious to obtain repeated observations of various objects enrolled in my Cycle, it became desirable for me to repair to Hartwell as often as these came into apparition; and it were ungrateful to omit adding, that the observatory was always most obligingly kept in readiness for my immediate and particular service. The measures and re-measures thus obtained with my former instruments are consequently all taken with the same eye, micrometers, and object-glass, and mostly with the same eye-piece power; and the diurnal motion of the earth was eliminated by the same practice in the use of the AR-handle, or the equable movement of the equatorial clock, as manipulated at Bedford. By these means, whatever optical or other bias might obtain, the results are assuredly comparable with each other, in evidence of angular movement and changes of distance, indicated by the operations of different nights and different years.

Some of these re-examinations have already appeared in my Cycle, which was published in 1814; but it is proper to reprint them here, together with those since observed. They are arranged in the manner already explained in that work (vol. i. p. 427, &c.); so that I need only remind the reader who may be unable to make reference to it, that the weights attached to the distances and to the angles of position-as the relative situation of two component stars in respect to the fixed circles of the sphere is termed-depend, according to the observer's judgment, on the number and presumed goodness of the observations. Thus, while 1 indicates an indifferent single measure or mere estimation, 10 is used to express that the astrometer is entirely satisfied with all the conditions of the operation. The last is a weight but too rarely obtainable; still, from having full leisure and a free choice of objects and opportunity, I was generally enabled to give the Hartwell measures high weights. The following is a list of the double-stars thus re-observed.