ART. V.-Description of a Tertiary Rainbow; by CHARLES HARTWELL.*

On the 28th of July, 1851, the writer observed, from the Theological Seminary, in South Windsor, Conn., what he judged to be a Tertiary Rainbow. After a heavy shower, and a little before sunset, the sun appeared, painting on the dark clouds in the east a beautiful primary bow. At the same time an appearance of decomposed light was seen in the N. W., upon a cloud of not very large dimensions, but from which rain was evidently falling. To the S. W., also, upon clouds somewhat separated, decomposed light was visible.

The appearance north of the sun was very bright, though in it were observed only the various shades of red and orange. It extended, according to my judgment, a degree or more in horizontal width, and from five to ten degrees upward. To the south the phenomenon was less brilliant, less in width, but distinctly traceable for some fifteen degrees from the horizon. Had these phenomena appeared in the east, no one would have doubted but that they constituted the two ends of a rainbow. The curvature of the colored light, and the correspondence in position, would have been sufficient proof. But as they were seen in the west, on the side with the sun, and tertiary bows are very rarely seen, it may be necessary to give the reasons which convinced me that I had really seen one. The phenomenon to the north was first observed, and filled the beholder with astonishment. What this appearance could be, so much more brilliant than ordinary views. of the sun's shining on clouds, and then, too, not on the edge but near the middle while the rest appeared as clouds ordinarily do, at the same time no reason being manifest from the position of the cloud and sun and the state of the intermediate heavens why the sun should shine on that part rather than another, not a little puzzled him.

On going to another window, the phenomenon to the south was seen. From its greater length, curved form, and its position on the opposite side of the sun, the conclusion was immediately drawn that they were the two ends of a rainbow. Recalling some instructions of my former teacher, Prof. Snell, of Amherst

*Messrs. Editors.-The accompanying paper was prepared by Rev. Charles Hartwell, now connected with the mission in China, to be read at the meeting of the American Association in Albany, 1851. Being unable to attend himself, he sent it by a friend, who was, however, obliged to leave before the day assigned for its reading. Ill-health and pressing engagements prevented his giving further attention to it, till he was on his voyage to China; when, lighting upon the notes, he transmitted them to me, to be disposed of as I should think best. Though more than two years have elapsed since the phenomenon herein described was observed, I think the account of it ought, even now, to find a place in some public record. Yours truly, E. S. SNELL.

Amherst College, Nov. 11th. 1853.

College, the thought flashed into my mind that this was a tertiary bow. Not recalling the dimensions of such a bow, I measured off the heavens as best I could, and judged the radius as seen to be about 40°. I have since learned that the radius by calculation is 40° 40', so that my judgment, correct or incorrect, agrees very well with the true dimensions of the bow.

Having stated these facts to Prof. Snell, and requested a brief communication from him, he kindly furnished one, which I ap pend to this paper.

"Amherst College, Aug. 15, 1851.

Since hearing you give an account of a phenomenon which you observed and supposed to be a tertiary rainbow, I have examined my notes upon the subject, and am well satisfied that you were not mistaken. All the circumstances forbid the supposition that it was a halo formed in prisms of ice. You estimated the

distance of the arcs from the sun to be 40°; this differs but about half a degree from the radius of the tertiary bow, as determined by calculation. The arcs were seen also in masses of falling rain of such limited thickness, that the light might well be supposed to have been transmitted through the rain to the eye.

Though the appearance was not one of remarkable splendor, yet you may congratulate yourself, I think, on having witnessed a phenomenon of the most rare occurrence. The writer of the treatise on Optics, in the English Library of Useful Knowledge, speaking of the bows caused by three or four reflections in each drop of rain, says, 'none of these bows, however, have been seen.' Professor Forbes, of the University of Edinburgh, in his learned Report on Meteorology to the British Association, 1840, remarks, 'These, the ternary, quaternary, &c., rainbows, have been long theoretically known, though rarely, if ever, observed in nature. The ternary rainbow ought to be about 41° from the sun, but is generally stated to be too faint to be visible. Two observations by Bergmann are the only recorded ones I have met with. Kæmptz observed a ternary amidst the spray of the falls of Schauffhausen."

Kæmptz, in his course of meteorology, after speaking of the bows of the third and fourth order, adds, but the intensity of these two latter is so feeble that they are rarely seen;' and puts in a note the following quotation, ' M. Babinet, when in the most favorable circumstances, on Mount d'Or, and on the Canigou, vainly endeavored to perceive them.'

It is obvious, as these quotations show, that the phenomenon which you witnessed is as rare as it is interesting. It seems to me highly probable that there is yet no public record of an instance in which an American observer has seen a rainbow on the same side of the heavens with the sun."

SECOND SERIES, Vol. XVII, No. 49.-Jan, 1854.

8

ART. VI.—The Earl of Rosse's Telescopes, and their Revelations in the Sidereal Heavens; by Rev. W. SCORESBY, D.D., F.R.SS.L. & E., etc.*

In a second lecture on these interesting subjects, recently delivered at Torquay, much and important consideration was given to the inquiry,--What has the gigantic telescope done?

The lecturer having himself had the privilege of observing on different visits, and for considerable periods, with both the instruments, was enabled to reply, he hoped in a satisfactory manner, to this inquiry. His opportunities of observing, he said, notwithstanding interruptions from clouds and disturbed atmosphere, had been somewhat numerous, and, not unfrequently, highly instructive and delightful. Of these observations he had made records of nearly 60, on the moon, planets, double stars, clusters, and nebulæ. He had been permitted also to have free access to, and examination of, all the observatory records and drawings, so that he was enabled on the best grounds, he believed, to say, that there had been no disappointment in the performance of the instruments; and that the great instrument, in its peculiar qualities of superiority, possesses a marvellous power in collecting light and penetrating into regions of previously untouched space. In what may be called the domestic regions of our planet-the objects in the solar system-all that other instruments may reveal is within its grasp or more, though by the prodigious flood of light from the brighter planets, the eye is dazzled unless a large portion is shut out.

But in its application to the distant heavens and exploration of the nebulous systems there, its peculiar powers have, with a steady atmosphere, their highest developments and noblest triumphs. In this department-that to which the instrument has been particularly directed-every known object it touches, when the air is favorable, is, as a general fact, exhibited under some new aspect. It pierces into the indefinite or diffuse nebulous forms shewn by other instruments in a general manner, and either exhibits configurations altogether unimagined, or resolves perhaps the nebulous patches of light into clusters of stars. Guided in the general researches by the works of the talented and laborious Herschels-to whom astronomy and science owe a deep debt of gratitude-time has been economized, and the interests of the results vastly enhanced. So that many objects in which the fine instruments of other observers could discern only some vague indefinite patch of light, have been brought out in striking, definite, and marvellous configurations.

Among these peculiar revelations is that of the spiral form — the most striking and appreciable of all-which we may venture to designate "The Rossean Configuration." Its discovery was

* An abstract of a Lecture delivered at Torquay, November 15, 1852.-From the Edinburgh New Philosophical Journal for January, 1853.

at once novel and splendid; and in reference to the dynamical principles on which these vast aggregations of remote suns are whirled about within their respective systems and sustained against interferences, promises to be of the greatest importance.

One of the most splendid nebulæ of this class-the great spiral or whirlpool-has been figured in the Philosophical Transactions for 1850. It may be considered as the grand type and example of a class; for near 40 more, with spiral characteristics, have been observed, and about 20 of them carefully figured. Dr. Scoresby had the pleasure of being present at the discovery of this particular form in a nebula of the planetary denomination, in which two portions following spiral forms were detected. Its color was peculiar,-pale blue. He had the privilege, too, of being present on another interesting occasion, when the examination of the great nebula in Orion was first seen to yield decisive tokens of resolution.

In these departments of research, the examination of the configurations of nebulæ, and the resolution of nebulæ into stars, the six-feet spcculum has had its grandest triumphs, and the noble artificer and observer the highest rewards of his talents and enterprise. Altogether, the quantity of work done, during a period of about seven years,-including a winter when a noble philanthropy for a starving population absorbed the keenest interests of science, -has been decidedly great, and the new knowledge acquired, concerning the handiwork of the Great Creator, amply satisfying of even sanguine anticipations.

Dr. Scoresby found, in September last, that about 700 catalogued nebula had been already examined, and transferred to the ledger records from the journals of the Observatory, (comprising only a selection from the general observations,) and the new nebule, or nebulous knots, discovered merely incidentally, amounted to 140 or more. The number of observations, involving separate sets of the instrument, recorded in the ledger, (exclusive of very many hundreds, possibly thousands, on the moon and planets,) amount to near 1700, involving several hundreds of determinations of position and angular measurements with the micrometer on the far distant stars. The carefully drawn configurations, eliciting new characteristics, exceed 90, and the rough or less-finished sketches amount to above 200. Of the 700 catalogued nebulæ already examined, it should be observed, that in full one-half or more, something new has been elicited.

In speaking of the effects of the flood of light accumulated by the six-feet speculum of the Earl of Rosse, Dr. Scoresby remarked, that this peculiarity of the instrument (connected as it is with due length of focus and admirable definition) enabled it to reach distances in space far beyond the powers of any other instrument. This was its peculiar province; and in this, as to existing instruments, there was not, nor, as he hoped to shew, could there be,

any competition. For comparing the space-penetrating power of the six-feet speculum with one of two feet (which has rarely been exceeded) we find it three to one in favor of the largest, with an accumulation of light in the ratio of 62 to 22, or 9 to 1. On comparing the powers of this magnificent instrument with those of a refractor of two feet aperture, the largest hitherto attempted, we have a superiority-making a due allowance for the loss of light by reflection from two mirrors, and assuming an equal degree of perfectness, figure, and other optical requirements in the refractor, and no allowance for absorption of light-in the ratio of about 4.5 to 1, as to light, and as 2 12 to 1, as to the capability of penetrating space, or detecting nebulous or sidereal objects at the extreme distance of visibility. Hence, whilst the range of telescopic vision in a refractor of two feet aperture would embrace a sphere in space represented by a diameter of 2; the six-feet speculum (assuming both instruments to be of equal optical perfection, magnifying equally, and allowing fifty per cent. for loss of light for two reflections in the one case, and none (?) in the other) would comprehend a sphere of about 4.24 diameter, the outer shell of which, 1.12 in thickness, being the province of the great instrument alone. But let us reduce these proportions to sections of equal spaces, that we may judge more accurately of the relative powers. Now, the solid contents of different spheres, we know, are in the ratio of the cubes of their diameters. Hence the comparative spheres, penetrated by the two instruments rereferred to, should be 4.243 to 23; that is, as 9.5 to 1. Deducting, then, from this vast grasp of space the inner sphere, capable of being explored by other instruments, we find that, out of nearly ten sections of space reached by this telescope, there are nearly nine sections which the six feet speculum may embrace as peculiarly its own!

What its revelations yet may prove, then, we can have no idea. Several thousands of nebulæ have been catalogued: the great reflector might add to these tens of thousands more. But this, seeing how few nights in a year are favorable for the highest powers, must be the work of years of perseverance. It would be a worthy undertaking for the government of a great country, to afford the means of multiplying such gigantic instruments. Application is to be made, in this direction, for a six-feet reflector at the Cape of Good Hope, for the examination of the heavens towards the southern pole. Lord Rosse, with his usual nobleness of liberality, will yield up his laboratory, machinery, and men, to the service of government, and is willing, moreover, to give the direction and guidance of his master-mind. Will the British nation be content with a refusal ?

The range opened to us by the great telescope at Birr Castle, is best, perhaps, apprehended by the now usual measurementnot of distances in miles, or millions of miles, or diameters of the