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I mention this circumstance, because Mr. Banson has said in No. l3 of the Gnanmos IN SCIENCE, when speaking of Melaniae, “ Ihave never met them in jheels or standing waters, so that they may be strictly called fiuviatile."
I have not yet had an opportunity of procuring any of these shells alive, from rivers: the only two living specimens in my collection were taken—thepone from a muddy nullah, the other from a well.
, Shell thin, fragile, diaphanous. Found in abundance in the Jegu nullah at Chunar, also I inmnost
jheels. Fresh-water Bivalves.
Found in nullahs at Chunar; also in tanks. Length of my largest specimen 2% inches; epidermis greenish brown; beaksdecorticated; Interior, beautifully nacreous.
Found at Chunar in nullahs and tanks. Beaks decorticated ; epidermis dark-brown. These shells are generally tuberculated interiorly, presenting an appearance of small pearls. The pearly texture of the inte
rior is often coloured with a pinkish tinge. No. 20.—UmoP
In rivers, nullahs, and tanks. Plentiful in the J egu nullah at Chunar. Epidermis yellowish or pale brownish green. Beaks naked. More solid than the preceding, and the interior lustre more brilliant.
Can this be the young of Unio No. 18 ?
sand-banks on the Ganges; they are easily traced by the tortuous fur_ rows which they leave on the sand. They are very slight, and the inte
rior appears to be satiny.
Epidermis olive-brown, and in some, of d.ifl'erent- shades of olive-green. Transversely furrowed; beaks sometimes pale purplish, sometimes do.
No. 23.--VAR. Epidermis pale yellow, or dirty straw-colour.
In the Ganges at Mirzapoor.
Some specimens brownish, others_ pale yellowish, with longitudinal
rays or stripes of brown.
Found at Mirzapoor in the Ganges.
These are all I have yet collected.
I have sent a few of each kind, except ‘Nos. 10 of the: Land Shells, and 6, 15, 16, and 25 of the Fresh-water Shells. Of some of those sent I have so very few that I could only spare one or two, without making my cabinet very bare. The poorness of the specimens therefore I hope you will excuse for the present, and should you not already possess suflicient, I shall have pleasure in sending more whenever lucky
enough to fall in with them. Should any part or the whole of the present communication be too
trifling for the pages of your Journal, do not hesitate an instant in rejecting it. My object in writing, not being for the sake of seeing myself in print, but for the purpose of communicating facts, in the cause of truth.
Neemuch, 20th October, 1833.
The specific names aregiven in my cabinet to enable me to distinguish them, and I have here inserted them, for the sake of reference should you notice them. Those marked (mihi) I have myself given. The others are those of Authors, -and given where I thought they be
* When we are able to furnish a plate of these shells, the present figures of reference shall be preserved.-En.
VI.——A Catalogue of Stars to be observed with the Moon, in March and April, l834,with the view of determining the diference of longitude of the places whereat they may be observed. By John Curnin, Esq. F.R.A.S.
Of all the methods which have hitherto been devised for the determination of the ditference ‘of longitude of any two places on the surface of the earth, it is now agreed on, that that dependent upon the observed interval of time which elapses between the transit of the moon's limb and of a star, having the same declination as the moon, is the most
accurate, certain, and expeditious.
It is the most accurate, because it involves no data but the rate at which the moon’s right ascension increases in the interval between its passing over the two meridians : it is the most certain, because it can be put in practice, at least twelve times in each lunation : it is also the most expeditious, because as many stars as may be agreed upon, and as are especially fit for this purpose, may be observed at both observatories on each night; each of which, if a corresponding one has been made at
the other observatory, being independent of the others, serves to give an independent estimate of the longitude.
It does not seem necessary that I should give a detailed account of this method- of determining the longitude, because that has been ably done by Mr. BAILY in the Memoirs of the Astronomical Society; nor that I should insist on the accuracy and value of this method, as both seem to be attested by the fact, that for the first time a catalogue of moon-culminating stars has been inserted in the Nautical Almanac for this year: but inasmuch as I have ventured to insert some stars in the accompanying catalogue, which are expressly rejected in the report made by the Committee of the Astronomical Society, relative to the improvements to be introduced into the Nautical Almanac, I feel it necessary to insert here that portion of the report, in order that it may be compared with my reasons for deviating from its implied injunction, and which, I trust, will be deemed sufiicient by resident observers in India :
“ The Committee stronglyrecommendthe insertionof the list of moon-culminating stars, given in the late Supplements to the Nautical Almanac, as aflording one of the best modes of determining the longitude of distant places, when the navigator, furnished with a transit instrument, can obtain a landing. As it is absolutely essential, however, that only one list of such stars should be published for the use of navigatorsof all nations, and as Professor Encke proposes to discontinue his list as soon as he is assured that the British Government will permanently adopt one, the Committee trust that they may be excused for entering rather more minutely 'into the mode in which those stars should be selected. They recommend, therefor-e,that notmore than four stars should be selected for one day, two of which are to precede and two to follow the moon: that the stars thus forming each pair be chosen so as not to be very distant from each other in right ascension, and nearly midway between the right ascension of the moon at the time of her transit on two consecutive days: that the two stars chosen to follow the moonon onedaybeadoptedas the two to precede the moon on the subsequent day : that no star be selected below the 5th, but on no account below the 6th, magnitude: that the stars so chosen should not be situated more than five degrees from the path of the moon’s true orbit : and that the list should be continued through each lunation within four days of the new
moon: that theapparent right ascension (in time) of the star to two places, and the mean declination of the star to the nearest minute, be given.”
In the first place, those stars recommended by the council are intended for universal use, and as being the most likely to be visible in ordinary states of the weather in places having variable climates. The number of these stars seem to me to have been selected with reference to fixed observatories, wherein a few observations being made on each night of every lunation for a considerable interval of time,would eventually assign the difference of longitude between them with the utmost accuracy: whereas, those in India, with one exception, may be aptly called flying observatories. It has seemed to me to be desirable that we should be enabled to determine the difference of longitude of these, in the shortest interval of time; and therefore, for this reason, and from the consideration that the climate will interpose no serious obstacle to their being observed, I have inserted. those stars which are so expressly repudiated by that report.
Another motive for forming this extended catalogue has arisen from this consideration, that those stars inserted in the Nautical Almanac have been selected with regard to observatories wherein astronomers or their assistants are expected to spend their nights, and who, therefore, are supposed to endure no pain and to forego no pleasure to be prepared to make those especial observations at all hours ; whereas, with the exception already referred to, observers here have other duties of a civil, political, or military nature to fulfil, and may, therefore, however willing,
be unable at all times to attend at the proper hour of the night to
make those observations, and those correlative ones whereby the error of their time-pieces, and the deviation of their instruments from the meridian, may be determined.
For these reasons, and for others, whichwill easilysuggest themselves,
Ihave ventured to draw up the accompanying extended catalogue ; but from which it will be observed, that the interval of time necessary to devote to the transit will seldom exceed one hour. If, however, gentlemen would observe those stars which are inserted in the Nautical Almanac, and which I may have omitted, they would essentially promote our geo» graphical knowledge in India, as their observation, combined with those
which are sure to be made in Europe, would enable us to fix the longi~ tude of places here relative to the principal observatories in Europe.
With the view of holding out every possible inducement to gentlemen to make these observations, I have inserted the apparent right ascension of the stars, although so far as this method of determining the longitude is concerned, the mean places would have answered equally well; and if inserted, would have saved me much trouble. But asgen~ tlemen in India, for whose use this catalogue is intended, may not have accurate time-pieces, nor sufiicient leisure to determine the errors of them, or the deviation of their instruments from the meridian, I have inserted a few stars which it appeared to me could be observed without in any manner trenching upon the time necessary for the other observations, and which if observed would enable us to determine the error of the time-piece and the deviation of the instrument from the meridian at the time of making these observations, and thus to render the kind of watch employed but a matter of secondary consideration.
The certainty with which the longitude can be deduced by this method appears to me so great, as to induce the conviction that many gentlemen would gladly make an extensive series of such observations, if they saw the chance of corresponding observations being made to confer a value upon their labours : and, as they may rest assured that those observations will be cheerfully made by Mr. Taylor of the Madras observatory, they will be sure of having at least one point of reference besides those which their own labours will create. With the view then of affording all the aid which circumstances at present place at my dis. posal, I send you the accompanying catalogue, and will continue to prepare others for circulation in succession through the same channel, till
experience shall have convinced me of the propriety of discontinuing them.
I have but one more remark to make—-and that is, that it appears to me to be most desirable that gentlemen should transmit their observations as they are made, which you could arrange in the form of a table, and publish for general information. In this manner all parties would be ena-. bled to compare their own observations with those of others, and assign a cause for any anomaly which these comparisons should point out. To make these observations of permanent value, I shall, I trust, be excused for stating, that it appears to me to be very desirable that the spot whereon they are made should be more accurately defined than similar observations made in other places have hitherto been :—that, in short, an exact measurement of the distance of the observatory from some remarkable and natural objects should be given, so that the position of these, and of the observatory, should be permanently preserved.