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been, in some cases, suspected to arise from local attraction, and which, while the level and plumb-line are used for determining the point of departure, it is impossible to detect. Very little, however, can be said on this subject till we are furnished with the necessary data. In the mean-time, we are happy to find that it is the intention of the Astronomer-royal to avail himself of the extreme accuracy of his new instrument to examine Dr. Bradley's tables of refractions, which are suspected, both by the French and the English astronomers, to require some modification; and should Mr. Pond succeed in making the necessary corrections relative to this subject, he will doubtless render an essential service to the science of astronomy.

With regard to the mechanical part of the observations which form the contents of these papers, we cannot doubt that the author's attention and assiduity have been equal to that which the importance of the subject required: but we do not observe that complete degree of accuracy in the detail which we could have wished to have seen. Thus, for example, the obliquity of the ecliptic, as ascertained by direct measurement from Polaris, is stated to be 23° 27′ 52",25, and, as drawn from the usual method, 23° 27′ 52′′,10: agreeing with each other, as Mr.Pond states, within a quarter of a second. This latter, however, depends on assuming the arc ZP 38° 31′21',15; which, in the author's account of his observations of the winter-solstice, he assumes at 38 31′ 21′′,5: an alteration which he has been induced to make from the mean of 120 subsequent observations of Polaris. The summer-solstice, thus corrected, gives for the obliquity, January 1st, 1813, 23° 27′ 515: whereas the same, as deduced from the observations of the winter-solstice, gives this obliquity only 23 27 4735; differing from the former by nearly 4, which the author calls a small discordance, that may be easily reconciled by a slight modification of Bradley's refractions, and to which principle it may perhaps ultimately be necessary to have recourse for its explanation.' In referring to the following summer-solstice, however, it seems that the original results require a still more important alteration; the correction of the sun's latitude having been taken +0,95, instead of —0′′,6: which reduces the original obliquity from 23° 27' 52′′, 25, to 23° 27' 50, 5, according to the author's statement: though we cannot find that either this or his other result, as drawn from the usual observations, brings out precisely the above quantity. Mr. Pond may term these very mall errors, as he does in speaking of the latter, though it amounts to more than a second and a half;-and as he does in his account of the discordance of the winter and summer-solstices, though

he

and as he does

he makes it amount to nearly four seconds;
again in a correction of a second in the north polar distance of
Procyon-but, small as they may be, they will, if frequently
repeated, tend very much to shake that confidence which we
ought to repose in the observations and computations of the
Astronomer-royal.

On the Light of the Cassegrainian Telescope, compared with that of the Gregorian. By Captain Henry Kater, Brigade-major. — This memoir relates to a subject of great moment in practical astronomy, and will no doubt engage the serious attention of all such observers as possess the means of repeating the experiments of the author. They are thus detailed:

The Cassegrainian telescope, from its first invention to the present time, has generally been considered to be merely the Gregorian disguised, and to possess no other advantage over it than the capability of being made shorter with the same magnifying power. This opinion, joined to the inconvenience of its inverting the object, has caused it to be thrown aside, perhaps too hastily, and without a sufficient examination of its properties.

As the experiments which I am about to detail may possibly lead to important conclusions, I shall perhaps be pardoned if I relate the circumstances which induced me to engage in them.

'A self-taught artist of the name of Crickmore, who resides at Ipswich, had, by exclusive attention to the subject, brought the Gregorian telescope to a degree of perfection surpassing any thing of the kind I have ever yet met with. Some months since, in the course of his experiments, he first completed a Cassegrainian telescope of one foot in length; and on viewing Jupiter with it, with a power of about Ico, I was instantly struck with the brightness of the image, far exceeding what might have been expected from the aperture; but I supposed this to have been a deception arising from the specula being more exquisitely figured than usual, which, producing greater distinctness, occasioned the idea of superior light. A short time after this, the same artist received an order for another telescope, which, from the success that had attended his recent efforts, he recommended to be of the Cassegrainian form. The aperture was five inches, the length thirty inches, and with a power of near 400 the image was so perfectly distinct and luminous, that I could no longer hesitate to conclude that, from some unknown cause, the Cassegrainian telescope actually possessed far more light than the Gregorian, and I waited most anxiously for an opportunity of verifying this, and determining the difference by experiment.

Such an opportunity soon presented itself, and under circumstances peculiarly favourable, as another excellent telescope of the Cassegrainian form was made, and I was fortunate enough to procure The mira Gregorian made by Mr. Crickmore some time before. rors of both these telescopes were cast at the same time, and from the same pattern, so that no difference of light could arise from any dif ference in the composition of the metal. The magnifying power of

both

both instruments was ascertained by experiment to be very nearly equal; but the excess was rather on the side of the Cassegrainian.

The telescopes being placed side by side, were directed to a printed card, at the distance of fifty yards; and on viewing it, the far superior brightness of the image in the Cassegrainian was strikingly apparent. Having prepared a circular piece of paste-board to close the end of the Cassegrainian telescope, I drew a number of concentric circles on it, at the distance of the twentieth of an inch from each other. The paste-board was then placed in the end of the tube, and an aperture was made, which was enlarged by cutting out one circle after another till the card appeared equally bright through both telescopes, and of this the eye judges most accurately.'

The Brigade-major then states the result of several experiments, from which it appears that the light in the two telescopes was equal when the area of the aperture of the Cassegrainian was to that of the Gregorian in the ratio of 4.632 to 10.871; and consequently that, when the apertures in both are the same, the proportion of light will be nearly as 7 to 3. A difference of such magnitude, he very justly observes, ought not to be admitted without extreme caution; and it was suspected that the polish of the great mirror of the Gregorian telescope might not be quite so perfect as that of the other, in consequence of its having been made some time longer than the latter: but this doubt was removed by a comparison of the same Cassegrainian with a new and very perfect Gregorian, made by the same artist, from which it was found that the light of the former was to that of the latter, with the same aperture, in the proportion of 3 to 2.

In the first experiment, it is observed, the advantages of polish might perhaps be on the side of the Cassegrainian telescope: but, in the latter, they were much in favor of the Gregorian. A mean, therefore, of both results may probably be considered as approaching the truth; and the light of a telescope of the Cassegrainian construction may be taken, compared with that of a Gregorian of the same aperture and power, at about 60 to 33.

A fact so new,' says the author, naturally leads the mind to hazard a conjecture as to the cause. In the Gregorian telescope, a column of light from a point of the object is received on the large mirror, and reflected in a cone of rays, the vertex of which is its focus, where an image is formed. Here all these rays meet in a single point, and, crossing each other, fall on the small concave mirror, whence they are again reflected, and form another image near the eye. Now, if light be supposed to consist of particles of matter, is it not possible that these particles, crossing in the same point, may interfere with each other? or, when thus forced within a certain distance of each other, may not a power of repulsion exist, which would occasion many

of

of them to be dissipated? In the Cassegrainian telescope the rays reflected from the great mirror are received by the small convex mir. ror before they arrive at their focus, and are consequently reflected back without having crossed as in the Gregorian. The conclusion then seems to be, that, wherever an image is formed,, much light is lost, and this conclusion perhaps derives additional force from a circumstance noticed in most elementary works on optics, viz. that the satellites of Jupiter and his belts may be distinctly seen with a Galilean telescope, whilst, with an astronomical telescope of an equal aperture and power, they remain invisible."

How far this explanation may be satisfactory we shall not decide: but the fact itself must be considered as of importance sufficient to attract the attention of opticians and astronomers, and may probably lead to very interesting results.

Papers in MEDICINE, CHEMISTRY, PHYSIOLOGY, &c.

PART II.

An Account of some Organic Remains found near Brentford. By the late Mr. William Kirby Trimmer. This paper contains an unadorned and interesting account of the extraordinary organic remains which have been found in the neighbourhood of Brentford. The strata are described as being, 1st, a sandy loam, 2d, sandy gravel, 3d, calcareous loam, 4th, gravel containing water, and, 5th, the extensive layer of blue clay which stretches under the metropolis and all its vicinity, at the depth of about 200 feet below the surface of the level land. No organized remains are found in the first stratum; the 2d presents some shells and small mutilated bones; in the 3d, are large remains of the ox and deer; and in the 4th, are found the teeth and bones of the elephant, both of Asia and Africa, the teeth of the hippopotamus, and the bones, horns, and teeth of the ox. The remains of the 5th stratum are of marine origin. In another spot, not far from the first, where the strata are nearly the same with those which are enumerated above, the remains of the elephant, hippopotamus, ox, and deer, are chiefly found in the 3d stratum, viz. that of the calcareous loam. They are deposited in such great abundance, that, in turning over an area of 120 yards, 6 tusks of the hippopotamus have been found: besides the tooth and horn of a deer, the tusk and grinder of an elephant, and the horns and skull of an ox.

On a New Construction of a Condenser and Air-pump. By the Rev. Gilbert Austin. The mechanism of this instrument cannot well be understood without a reference to the plates which accompany it: but its principal merit seems to consist in the manner in which glass joints are connected together, so

as

as to be air-tight, without the intervention of any moist substances which might interfere with the results of the experi ments performed with the machine. The description is drawn. up with a degree of prolixity which is always undesirable on such occasions, and often produces the obscurity which Mr. Austin has been anxious to avoid.

On the Formation of Fat in the Intestines of living Animals. By Sir Ev. Home, Bart. It is here observed that the great diversity in the size and structure of the colon, in different kinds of animals, having led the author to suspect that some important function in the economy of the living body was performed by this organ, he was induced by several analogies to conceive that their office consists in the formation of fat. He supports his hypothesis by the resemblance which exists between the situation of the contents of this part of the alimentary canal, and that of the muscular fibre when it is in a state of conversion into adipocire; and by the fact that substances of a fatty nature have occasionally been found in the colon: but he confesses that the strongest argument in its favour is that he is acquainted with no other mode by which fat can be formed. Perhaps our readers may not deem this kind of reasoning quite convincing. The paper, which is considerably extended and very discursive, consists of a relation of facts; some adduced from Sir Everard's own experience, and others furnished by Dr. Babington and Mr. Brande. Some experiments are brought forwards by the latter, in order to prove that the bile is the principal agent by which this change is effected; and it is implied that the formation of fat is one of the most important purposes which the bile serves in the animal economy. The whole communication is certainly not without interest, though we think that it is very far from being perfectly satisfactory.

On the colouring Matter of the black Bronchial Glands, and of the black Spots in the Lungs. By Geo. Pearson, M.D., F.R.S.It is well known that, in the adult human subject, the bronchial glands are generally of a black or dark blue color; and that spots or lines of the same hue make their appearance on the surface of the lungs about the age of 20, and continue to increase until nearly the whole superficies of the lungs becomes blackened. This black appearance has been conjectured to depend on the presence of carbonaceous matter: but the supposition had not been submitted to the test of experiment, and some considerations even seemed adverse to it. Dr. Pearson relates a series of experiments which he performed for the purpose of procuring the coloring matter in a separate state, and afterward reports the effects produced on it by different re-agents;

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