Графични страници
PDF файл

On the Use of a Simple Syphon as a Hydrometer. By Mr HENRY MEIKLE. Communicated by the Author.

AMONG the numerous instruments for comparing or ascertaining the specific gravities of liquids, the " pump areometer" has been for a considerable time known. This consists of a syphon, having its extremities immersed in two different liquids, whose specific gravities are to be compared, and having a pump or syringe communicating with the upper or bent part; so that on exhausting a portion of the included air, the atmospheric pressure raises the liquids through heights, which are inversely as their specific gravities. The reason of this is obvious, and was long ago particularly noticed by Boyle. In the last volume of the Philosophical Magazine, is a description of a different instrument, consisting of a double syphon, with four parallel legs ; into each pair of which, a different liquid being put, with a portion of air between, the effective columns compressing that air will be inversely as their specific gravities. This instrument possesses the remarkable property, that if the bore of the tube, however narrow, be uniform, its indications will be entirely free from capillary action; because both extremities of the same liquid being equally affected by capillary attraction, the difference of their heights, or the effective column, is not altered thereby.

It appears, however, that, when the liquids are transparent, the syphon may be applied in a still more convenient form than either of those just mentioned, though, to avoid capillary action, the tube in this, as well as in the pump areometer, must not be narrow. Thus, if the legs of a simple glass syphon be immersed in different liquids, the lengths of the columns, depressed by the included air, will be inversely as their specific gravities. The vessels containing the liquids only require to be transparent, such as glass bottles or jars. Any scale of small equal parts may be attached to the tubes; but it will be still simpler, and more convenient, for corrosive liquors to graduate the tubes themselves; for, in proper hands, a glass tube is as easily divided into equal parts as any thing else.

But with the assistance of a little calculation, the simple syphon may be used for comparing the specific gravity of an

opaque liquid with that of a transparent one, as for instance water.*

Let a be the volume which the air included in the syphon had under the external barometric pressure b, and c the increase of pressure occasioned by the immersion which will be proportional to c', the volume of air below the surface of the water; also let e be the volume of water in the bottom of the tube. Then the αι b+c

reduced volume of air is

liquid within the tube, is a —

and the volume of the other

[blocks in formation]

a b b+c

subtracted from g, the whole contents of the tube under the

level of the opaque liquid, gives g+e

a c


for the column

of air below the surface of the opaque liquid, and if by this we divide c', the quotient is the specific gravity sought.

In this case, it is supposed that the bore of the tube is uniform, and that both legs enter their respective liquids at the same instant. But when the two specific gravities are very different, unless care be taken not to immerse the syphon too far, some air may escape from the end which descends into the lighter fluid. This may also be avoided, by gradually lowering the vessel containing the heavier liquor, or raising the other whilst the syphon is descending; but that will seldom be necessary, and the escape of a little air will not affect the simpler method, to be used when both liquids are transparent.

On the Live Marine Cockles, said to have been found at a great distance from the Sea in Yorkshire. In a letter to Professor JAMESON. By W. C. TREVELYAN, Esq. M. W. S., &c. [Nearly a year ago, my intelligent friend Mr Witham of Lartington, had sent to him in Edinburgh several specimens of live marine cockles, said to have been found in a bog, considerably above the level of the sea, and fully forty miles distant

In some opaque liquids, as for example mercury, the top of the column within the tube may be rendered visible by bringing the leg of the syphon close to the side of the jar; in such cases, no additional calculation is required.

from the sea coast. Since that time, Mr Witham visited Yorkshire, personally examined the spot, and actually found live marine cockles, in the situation already mentioned. We are still, however, of opinion that the live cockles are not natives of the bog; and in this view we are borne out by the following statement of Mr Trevelyan.-ED.]

HAVING lately been on a visit in Yorkshire, in the neighbour

hood of the place where the marine cockles sent to Mr Witham were said to have been found, I took advantage of the opportunity to examine the spot, and to make inquiries concerning the fact. The result is my thorough belief, that the cardium edule is not a native of the place, and that if specimens of it have been found there, they have been put there by some absurd person, for the purposing of hoaxing the individuals who sent the statement to Edinburgh.

[ocr errors]

The spot where they are said to have been is a peat-moss resting on sand, through which drains have been cut. The tenant (Pratt) on whose farm part of the moss is situated, and who has been there many years, when I questioned him, said that he had seen cockles at different times in clearing out the drains, and described them as being nearly the size of his thumb nail, of the colour, and about the same thickness as the whelks, which are common in the ditches there, some of which he shewed me, and which are fresh water helices (putris, &c.); that the stripes were across the shell, from side to side, not in the same direction as in the sea-cockle, which he said he knew well, but had never seen any, or heard of any being found there, excepting those sent to Mr Witham. From this description, I was convinced that Pratt's cockles were the Tellina cornea; the only cockles I expected to find there, and of them, after a little search in the ditches, I found some small specimens. They call them cockles, from their analogy to the marine shells of that name, in the same way as the helices are called whelks.

The farm house called Cocklesbury stands on an elevation, a short distance from the moss; and may perhaps be named from the cockles (Tellina) found there, though I think if it is from shells at all that it derives its name, it is from the shells abundant in the neighbouring limestone, some of which may perhaps

have been dug up in sinking the foundations. We have in Northumberland a limestone abounding in Terebratula and Anomia, the local name of which is the Cockle-shell limestone.

In a moss much resembling this, at Kirby Ravenswath, in the same neighbourhood, now draining, I found the same shells below the peat, which is about four feet thick, resting on a sandy clay. Formerly it has evidently been covered with water, forming the principal defence of Kirby Ravenswath Castle, which it partly surrounds.

Notice of Fresh Water found in the Sea at a great distance from the land. By D. BUCHANAN, Esq. (In a Letter to Professor Jameson.)

I HAVE received

HAVE received your letter of the 15th, in which you request me to give you an account of my voyage to Chitagong, during which the singular circumstance of our finding fresh water so far from land occurred. Not having thought much of this at the time, I fear I may have forgotten some of the circumstances attending it, but all that I do recollect shall be communicated to you. In the beginning of September 1824, I embarked with the other officers of our regiment, in a country ship (having most of the officers of his Majesty's 54th Regiment on board), for Chittagong. We sailed out of the Madras Roads with a fair wind, which continued for four days; but, on the fifth, we were becalmed, and continued so for fourteen days, having had only once or twice a very slight breeze, which never lasted longer than a few hours. It was towards the end of this calm that I observed a very strange appearance on the surface of the glassy ocean. It seemed to be furrowed in several directions, and much agitated in these furrows, so that, when the ship was drifted into these parts, she was driven about in all directions. On the night of the 14th, a breeze sprang up. Owing to our unexpectedly tedious passage, we ran short of provisions, particularly of water. You may suppose what was our joy and astonishment the next morning, in taking up the water alongside to wash decks, to find that it was fresh, and much more palatable than that which remained in our casks, which were imme

diately replenished with it. By this day's observation we were 125 miles from Chittagong, and about 100 from the nearest part of the Junderbunds. The water was of a more yellow tinge than in most parts of the bay; and those who drank a great deal of it, suffered from it afterwards.

Description of Anatina villosiuscula, a new Species, and of Venerupis Nucleus, a Species new to the British Fauna. By Mr WILLIAM MACGILLIVRAY, M. W. S., &c. With Figures. Communicated by the Author.


Pl. I. fig. 10, 11.

Spec. Char.-A. TESTA ovata ventricosa, inæquivalvi, antice

subtruncata, rugosa, minutissime granulata.

Description.-Shell ovate, ventricose, inequivalve, with the umbones nearer the anterior extremity, the posterior extremity rounded, the anterior subtruncate, thin, fragile, diaphanous, transversely wrinkled, white, slightly tinged with yellow. Right valve larger, and much more convex, with a more prominent umbo; umbones directly opposite; ligament double, the external short. One transverse scarcely prominent tooth in each valve, resembling an incrassation of the margin, immediately behind which, and directly under the umbo, is a deep sulcus. Posterior extremity shut close, anterior hiant. External surface covered with very minute prominent points, which, to the naked eye, are not individually distinguishable, but aggregately produce a dull or lustreless appearance; internal surface smoothish, shining at the ends, glimmering about the middle.

It will be perceived that this shell is closely allied to A. myalis of Lamarck, which is Mya pubescens of Turton, as well as to several others, such as Anatina truncata of Lamarck. It would be tedious to enter into all the explanations necessary for the accurate distinction of species so intimately connected. Our British conchologists have sadly puzzled themselves with this genus, which they have most injudiciously stuck to the genus Mya, after Linnæus's example; so that, to clear up all difficulties, would require a monograph.

« ПредишнаНапред »