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not unfrequently happens that the greatest depression of the barometer succeeds to a considerable elevation of it, and vice versa, so as to exhibit a difference of this kind. In the instance of the remarkable depression of the barometer, in December, 1821, Mr. Howard informs us it sunk on the 25th instant to 27.83 inches, and on the 27th remained for twelve hours stationary at 28.07 inches; and from which time to the 31st, it rose to 30 inches. How many examples might be selected from the experiments recorded in the preceding pages, to prove that a difference of two inches in the barometer for 12 hours, would be sufficient to produce an alteration of rate; and there can be little doubt, that had the rates of some good chronometers been carefully attended to,* during this singular alteration of atmospheric density, variations of rate at least equivalent to that produced by transporting a time-keeper from London to Geneva, would have been observed. The sudden changes to which the density of the atmosphere is sometimes liable in this climate, renders it necessary therefore, that a correction should be applied to the rate of a chronometer proportional to the alteration of density; the correction partaking in some cases of a positive character, and in others of a negative. A similar correction must likewise be necessary when a traveller ascends to any considerable elevation above the sea; for example, to Geneva, to the plains of the Castiles, or to the table land of Mexico. The value of the correction will be dif. ferent for different time-keepers, and in all cases must be determined by previous experiment.
“The changes here alluded to can influence chronometers only beyond the tropics, since between them it is known, that the fluctuations of the barometer do nat much exceed a quarter of an inch; but in the arctic regions, where the causes which promote alterations of atmospheric density are the greatest, the effect on the time-keeper must be the greatest also. In proportion, however, as we ascend above the level of the sea, the uncertain changes of the barometer are known to approximate to uniformity; and therefore at higher elevations, the same chrono. meter would preserve a greater regularity of rate than in the lower regions of the air.”—p. 397.
It now became the subject of question, whether the alterations of rate displayed under the circumstances of the foregoing experiments, is acquired immediately on the change of pressure taking place, or whether any length of time is required to produce the effect. Numerous experiments showed that the former is the case.
Mr. H. tried a further experiment, to ascertain, whether the increase of temperature, generated by the condensation of air, had influenced the results. This was found not to have had any perceptible effect.
To account for these changes of rate, the most simple supposition is, that a change takes place in the arc of vibration of the balance, in consequence of the altered density of the air. If the adjustment of the balance were so perfect as to give an exact isochronism in its vibrations, the increase or diminution of the arc would not affect the isochronism, nor consequently the rate. But if, as must be the case in reality, the isochronism be in the slightest degree imperfect, this change in the arc will cause a change in the rate.
From the very delicate nature of the balance, an increase in the density of the medium, will tend to diminish its arcs of vibration. Mr. Atwood (Phil. Trans. 1794) gave an expression for the function which represents the daily aberration of a chronometer. It depends on the ratio of the original and disturbed arcs, affected by an exponent denoting the ratio between the elastic force
• I have attempted, but without success, to obtain the rates of some good chronometers during this period.
of the spring, and the angular distances from the point of quiegcence. It is shown, that according to certain alterations in these elements, the rate will undergo certain alterations. It appears, that if the supposition be that which accords with the elastic force of the spring being in a less ratio than that of the angular distances from the point of quiescence, then if the disturbed are be less than the original, the value of the function will be positive, or the chronometer will gain in condensed air, and vice versa. If on the other hand, we suppose the ratio of the elastic force of the spring to be greater than that of the angular distances, then in condensed air the value will be negative, and the chronometer will lose ; and vice versa.
Every reader will be struck with the extreme elegance of this application of mathematics to the physical problem. It at once points out to us a cause which will produce a change of rate on an alteration of density in the medium, and equally accounts for that singular circumstance, that the change should be of an opposite character in different instruments. Upon the whole, we cannot quit the subject, without recommending to the critical and mathematical reader, the whole paper, as a truly beautiful specimen of pure experimental inquiry in the first instance, combined with a subsequent application of the resources of analysis, leading at once to the true theory of a class of phenomena of no inconsiderable interest in a practical point of view.
Our remarks have already extended themselves to a greater length than, we fear, will be agreeable to many of our readers; we must, therefore, be very brief in our notice of the only remaining investigation to which we have to direct their attention. This comprises an example of the practical application of chronometers in some important determinations of longitudes. The
The paper is entitled, “ A Short Account of some Observations made with Chronometers, in two expeditions sent out by the Admiralty, at the recommendation of the Board of Longitude, for ascertaining the longitudes of Madeira and Falmouth, by Dr.J. L. Tiarks; No. 19." In these excursions, a point of very high importance in geography came into notice. Dr. T. by observations with numerous excellent chronometers, transported many times backwards and forwards between Dover and Falmouth, as also afterwards between Portsmouth and Falmouth, found the differences of longitude so deduced to be greater by several secopds of time, (on the former instance 4 sec. corresponding to 1 min. in distance), than those found by the trigonometrical survey. Having verified this remarkable discrepancy, by using every possible degree of exactness in his observations, the author enters upon some mathematical investigations, to point out how the error must have crept into the results of the survey. This he shows, took place in the mode of reducing the results for the sphericity of the earth; and points out, that the value adopted in calculating the survey for the earth's ellipticity is incorrect, whilst the results of his chronometrical observations agree very closely with the most exact determinations of the figure of the earth. This agreement will doubtless be very much in favour of the chronometers; and there cannot remain much doubt, that the error which Dr. T. has the merit of having pointed out, does really exist; but it may perhaps become a subject of question, after what has been ascertained respecting the changes of rate to which chronometers. may become subject, whether the variation in the pressure may not have been such in the intervals of these observations as to require attention, and to have been sufficient to cause some part of the difference.
SELECTED FOR THE MUSEUM
ON THE TRANSPORTATION OF FISH FROM SALT TO FRESH WATER.
(To the Editor of the Quarterly Journal.] DEAR SIR,-You expressed a desire to know the progress which has been made in the transplantation of fish from salt to fresh water, since the period at which I communicated the paper on that subject to your Journal. Mr. Arnold, who has carried on these experiments, at my wish, with great zeal, has succeeded in adding many more to the list; and, both in respect to the physical fact, and to the question of economy, the success has been far greater than any one was willing to believe.
The list of the additional fish will be seen by comparing that which is appended to this letter with the former one; and as the subject has excited considerable attention, you will perhaps not object to a statement which may attract even more, by presenting, in the form of a prospectus, the essential facts and arguments. It is only by placing them in this form that they are very likely to produce the effect which appears desirable.
I may now, however, subjoin some remarks which could not well find their place in such a statement, and which have been the result of more experience and attention.
It is certain that the flavour of every fish which has yet been tried has been improved; and I can vouch for the superiority of the basse, the mullet, the loach, the atherine, and the sole, from the pond, to those from the sea. This might be expected, for it is what happens potedly with respect to oysters.
The sole becomes twice as thick as a fish of the same size from the sea, and its skin also becomes extremely dark, or nearly black.
The plaise also increases materially in thickness, and loses its spots. In some cases, it appeared three times as thick as in the sea. The basse also turno much thicker, and improves in delicacy.
The mullet almost ceases to grow in length, but enlarges in breadth, and presents a much deeper layer of fat.
Crabs and prawns have found their own way into the pond; as
304 On the Transportation of Fish from Salt to Fresh Water. have loaches, and some other small fish; and while, formerly, there were none of the former two, the water is now absolutely swarming with them. Thus also, apparently, the eels have multiplied; as it is now easy to take a cartload at once, where formerly a dozen or two was a large capture. I have thus also more distinctly ascertained, and to the satisfaction of Cuvier, who had been unwilling to admit it, that there are two species of fresh-water eel, distinguished by the comparative acuteness and breadth of the nose.
I have lastly to add an observation inadvertently omitted in the former communication, which may be used as an à priori argument for the possibility of this transplantation. It is, that oxygen is much more easily disengaged from fresh than from salt water. Consequently, the act of respiration ought to be easier in the former than in the latter; and therefore it is not to be presumed, as it has been, that sea-fish cannot respire fresh water.
As I have given the shad without its Linnæan name, I think it right to add, that our shad is yet unnamed; because the Clupea Alosa is the Alose of the French, common in the Seine and on the coast of Normandy; a fish as good as our own shad is detestable, and a decidedly different species of this troublesome and ill understood genus. If I have given the vulgar term rock-fish, it is because I wish to reject the term wrasse, for the present, as it stands for a species; whereas the whole of this genus (labrus) is still in extreme confusion, and in one, which I hope to aid in rectifying, with the assistance of Cuvier's materials and our own species. I am yours, &c.,
J. Mac CULLOCH.
Prospectus of a Plan for Preserving and Rearing Fish for the
London Market. From various observations and experiments, of which evidence is subjoined, it has been found that sea-fish will live and thrive, and also breed, in ponds or enclosures; and, with regard to many, it also appears that it is indifferent whether the water is salt, or fresh, or brackish, or alternately fresh and salt.
It is also found that they may be fed in such enclosures, if necessary, as our domestic animals are; but that if sufficient numbers and kinds are placed together, they feed each other without requiring further care.
It is further observed, that every, or almost every species, improves in flavour and quality, as oysters are known to do under transplantation.
It is well known that, of all the fish brought to market, a very small proportion is in good condition, the rest being apparently ill fed; and hence the number of bad fish so well known to fishmongers.
It is much better known that, from bad weather, or other causes,
the supply of the market is very irregular. Thus the public suffers when the supply is short, and the merchant when there is a glut. It is not uncommon for a glut to come in London when the town is empty; and, on the contrary, for it to want fish when full.
The proposed plan, if executed, would bring the fish within our own power, to be taken alive when wanted, and, from being better fed, in greater perfection and more uniformly good. It would be like taking stalled oxen, instead of wild Scotch cattle. It would also enable the merchants to regulate the supply by the demand, and thus to satisfy better the public and themselves. The trade would be steady instead of precarious; as the prices to the public would also be. It would be conducted, directly, between the public and the grower, or with the intervention of one retailer only, and thus a heavy cause of complaint be removed. Lastly, the public would be always sure of fish, and it would be sure of them at moderate prices.
Such are the proposed advantages. As far as the species that' breed in such confinement, the fish would reproduce themselves, or a pond of this nature would resemble a common fish-pond. For those that will not, if there are any such, the ponds would be mere repositories for keeping alive, till there was a demand, the fish brought into them from the sea. They would also be feeding places, allowing bad fish to improve. Thus far, the fisheries would go on as before, and the fishing trade would consequently not be injured. It would be increased, on the contrary; because, with a better regulated market and more moderate prices, the consumption would be augmented. There can be no objection therefore on the score of injury to the fisheries. The plan is, virtually, one to preserve fish alive after being taken, instead of suffering them to waste, to render them better in quality, and to supply them more regularly.
The plan, therefore, is, to enclose, in any convenient part of the Thames (since the quality of the water is proved to be indifferent,) a space sufficient for the purpose. A dock, or an excavation in the nature of one, would be unnecessary, as the water itself, in many places not navigated, might be enclosed by a palisade. In this, the fish would be received from the fishermen, by means of well-boats, alive. Those which chanced to die would become the food of others. Many would breed, as they have been found to do, and thus also would produce food. But they might also be fed by means of butchers' offal, or other matters easily procured in a great city, as was the practice of the ancient Romans.
From the enclosure, the fish would be taken by nets, the kinds in demand, and the quantity, selected, and the bad fish also returned for improvement. A steam-boat would supply them to London daily, and to any market which might be established; and they might even be brought up alive, so that the unsaleable ones would not be lost. Vol. VII. No. 40.-Museum.