the common eel, and the barnacle, are similar in their mode of generation, every one of these animals impregnating itself.' Sir Everard believes that the conger and the common eel belong to the same species, and differ only in consequence of one living in fresh and the other in salt water. Their organs are similar. In the lepas anatifera, a species of barnacle, the ovaria are situated round the oesophagus, and may be mistaken for the salivary glands; while the penis may be considered as the oviduct for depositing the ova after impregnation. Subsequently to that event, the ova pass through a small opening in the outer covering, into the stem by which the body of the barnacle is suspended; and when the embryo is completely formed, it makes its way out laterally from the stem, leaving behind the shell or covering of the egg attached to the inside of the tube, marking the place from which it escaped; the young lepas acquiring a stem of its own. All these circumstances are well represented in drawings annexed. In the earth-worm, the manner of connection is like that of the leech rather than of the snail. The ova, after impregnation, are conveyed into cells, and there deposited till they are batched; and in them the young goes into the chrysalis state though it does not remain immured till the chrysaliscovering is expelled, but eats its way out. MATHEMATICS, ASTRONOMY, &c. Corrections applied to the great Meridional Arc, extending from Lat. 8° 9' 38".39 N., to 18° 3' 23".64 N., to reduce it to the Parliamentary Standard. By Lieut. Col. Lambton, F.R.S. It is known to our readers, that since the question has been agitated relative to the establishment of a new system of weights and measures, Captain Kater has taken great pains to compare with each other the different standardmeasures possessed by the Royal Society, the Court of Exchequer, &c.; and that the commissioners determined ultimately to adopt the scale that had been made by Mr. Bird, the relation between which and the French metre had been very accurately ascertained. Colonel Lambton, in the course of his survey in India, had made use of two different scales; the latter of which had been laid off from Ramsden's bar, and required a correction of +00007 to reduce it to the new standard-scale; and the former a correction of 000018 to reduce it to the same. The reduction of the different arcs forms the subject of this memoir, the results of which will be principally interesting; viz. the lengths of the arcs corresponding to the different degrees of latitude, and the compression thence arising: which are thus stated: 'The " Fathoms. 'The degree for latitude 9 34 44=60477,09 for latitude 13 2 55-60490,31 Indian. for latitude 47 30 46=60779,00 French. Then computing from Eq. 3., page 498., in the Philosophical Transactions for 1818, 2d Part, we shall have the ellipticity of the earth as follows: These fractions for the compression are highly satisfactory, when we consider the great difference in latitude between the extreme arcs; viz. 9° 34' 44", and 66° 20′ 12". Computing from the results thus obtained, Colonel Lambton finds the length of the degree on the equator, or in lat. 0, to be 60850-17 fathoms; and for the quadrantal elliptic meridian, from the equator to the pole, he obtains 5467756 fathoms. Now this length, divided by 10'000'000, gives the length of the French metre; and, reduced, it becomes 39-3677 English standard inches: whereas the French standard metre is 39.3709 such inches, both at the temperature of 62° Fahrenheit. Col. L. concludes by observing; It may be satisfactory to the mathematicians in Europe to know, that I am now advancing through Hindoostan; and, from what I can learn from the different public authorities, I do not apprehend any difficulty. They are all inviting in their letters, and all seem desirous that I should go through their respective districts. If my present arc be continued direct, it will pass through Bopaul, and near Seronje, where I shall have again to observe the stars and measure a base; and if Scindiah's country be in a quiet state, my meridian will pass near Gualior, his capital; and my sixth section will terminate near Agra, on the Jumna. I have made up my mind to execute all this if I live, and continue to have that flow of health and spirits which have hitherto attended me. The results of such an extensive measurement must be interesting to scientific men; and I shall exert my endeavours in doing justice to the work, and in giving a faithful account of the operations.' From From these concluding lines, in which the author speaks of his health in such favorable terms, every hope might have been reasonably entertained that astronomy and geodesia would still be enriched by his talents and indefatigable labours: but, alas! how uncertain are all human expectations! Before the present memoir had been read to the Society, this distinguished observer had already paid the debt of nature: but his name and memory will be long cherished by every lover of astronomical science. On the Changes which have taken place in the Declination of some of the principal_fixed Stars. By John Pond, Esq., Astronomer Royal, F. R. S.- Appendix to the preceding Paper. By the Same. On the Parallax of a Lyra. By the Same. All our astronomical readers are aware of the controversy which has been long carried on relative to certain changes observed in the situation of some fixed stars, which were supposed to arise from an annual parallax. Unless the stars be actually at an infinite distance, the diameter of the earth's orbit, which in round numbers may be stated at 190,000,000 miles, must subtend from each star a certain angle; which angle, if it amounted to any sensible quantity, ought to be detected by observations from the earth, at those times when the latter body is in opposite parts of its orbit. That such angle, if any, is very small, has always been allowed, and this circumstance was one of the strongest holds for those astronomers who opposed the doctrine of Copernicus: but this point having been long yielded, it became an interesting question to determine the existence or non-existence of a sensible parallax. At one time it has been admitted, at another denied; and indeed the quantity, if any, being unquestionably very inconsiderable, could not by possibility be detected except by the most accurate instruments and the best observers. The subject had for a long time remained in this state, when a few years ago Dr. Brinkley, of Trinity-College, Dublin, an excellent observer, and possessed of a very fine instrument, imagined that he had actually discovered a sensible parallax in certain stars. A question of so much interest to the science of astronomy, and proceeding from so respectable a quarter, engaged considerable attention; and corresponding observations were undertaken at the Royal Observatory of Greenwich. These, however, failed in detecting the change in question, and new means and new instruments were tried, which also failed. Dr. Brinkley repeated or rather continued his observations, which gave the same results as before, and the subject seemed still involved in doubt. It now appears probable, probable, however, that Mr. Pond has discovered that the cause of the difference observed, which had been attributed to parallax, is an error in the instrument, proceeding from a difference in temperature at the two opposite seasons of the year near the solstices. At all events, it is very remarkable that the parallax noticed by Dr. Brinkley is much greater in stars so situated as to have their maximum and minimum at these two seasons, than in those in which the same ought to happen at other times. On this head the astronomer royal observes: The reason, I conceive, why Dr. Brinkley does not find parallax in y Draconis is, that with respect to the zenith point, his instrument, like every one of a similar construction, is a perfect instrument. No portion of the arc is employed, nor can temperature here occasion any errors by its changes. As the star to be examined recedes from the zenith, the instrument becomes less and less perfect; and he finds a small parallax in a Cygni, a larger in a Lyræ, and oftentimes a still larger in stars more remote from the zenith. An additional reason for suspecting that the discordances observed arise from temperature is this: the greatest supposed parallax is found in those stars whose maximum and minimum of parallax would fall in the extreme seasons; and it is not at all improbable that irregular refraction, arising from the unequal state of the temperature within and without the Observatory, may have had a considerable share in occasioning the Dublin discordances, combined, perhaps, with the effect of the changes of temperature upon the instrument itself. It is a circumstance not hitherto sufficiently noticed by astronomers, that there are many cases where the smallest disturbing cause will produce an error quadruple of its own amount; and consequently, that the greatest error to which we are liable from such a cause at any one observation will be only one-fourth of the difference that we can detect between the most discordant of them. Of such a nature are those disturbances which, like refraction for instance, introduce errors, both positive and negative, into the determination of either extremity of the arc that measures the distance between two stars. By a singular combination of circumstances, not probable certainly when considered à priori, but by no means impossible, the variation caused by change of temperature may follow an annual law so little differing from that of parallax, as to bring out the assumed parallax, and to leave the solar nutation disengaged. Notwithstanding the importance of these investigations to the history of astronomy, and to our forming a correct notion of the system of the universe, yet our decision ultimately turns upon so very small a quantity, that our having reduced the enquiry to these narrow limits rather tends to show the perfection of each instrument than the defect of either. On former occasions I considered the question of parallax in the particular case of a Lyre as undecided, and as perfectly open to future investigation; but the observations of the present year have produced, on my mind, a conviction approaching to moral certainty. The history of annual parallax appears to me to be this in proportion as instruments have been imperfect in their construction, they have misled observers into the belief of the existence of sensible parallax. This has happened in Italy to astronomers of the very first reputation, The Dublin instrument is superior to any of a similar construction on the Continent; accordingly it shows a much less parallax than the Italian astronomers imagined they had detected. Conceiving that I have established, beyond a doubt, that the Greenwich instrument approaches still nearer to perfection, I can come to no other conclusion than that this is the reason why it discovers no parallax at all.' and We have hitherto principally referred to the last of the three papers whose titles are given at the head of this subject, because it is conceived that the matter there investigated led to the discovery mentioned in the two former, which may be thus briefly stated. If any correct catalogue of stars, as for example that of Bradley for the year 1756, be compared with a more recent one, as the Greenwich catalogue for 1813, it is possible to deduce the annual variation for each star for the mean period, on the supposition of an uniform proper motion in each; then, allowing for the change of precession for each star, a predicted catalogue may be formed for any subsequent year, as for example, the year 1822. Now such a catalogue being formed, and compared with the observed catalogue for the same year, the following difference will be found to subsist between them: The general tendency of all the stars will be to appear to the south of their predicted places, and this tendency seems to be greater in southern than in northern stars; if any star be found north of its predicted place, it will always be a star north of the zenith, and the quantity of its motion extremely small. There may be observed a much greater tendency to southern motion in some parts of the heavens than in opposite or distant parts as to right ascension, and in much the greater portion of the heavens the southern motion seems to prevail. A southern star, as Sirius, situated in that part of the heavens most favourable for southern motion, will be found more to the south of its predicted place than Antares, situated in the part least favourable for southern motion, though it is itself more southward. Several stars have moved more from their predicted places than other neighbouring stars; when this happens, the motion is always southward; I have yet met with no exception to this rule; not a single star can be found having an extra tendency to northern motion; and indeed the northern motion in any star is so very small, that it would never have excited attention. A very great deviation will be found in three very bright stars, Capella, Procyon, and Sirius: the proper motion of each of these 1 |