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retted hydrogen. The part of the plate of mica, containing the crust, should then be cut off, and introduced into glass tubes hermetically sealed up, like the slips of blotting-paper, containing the coloured results of the re-agents.

We think it scarcely possible, certainly not necessary for any practical purpose, that the processes

of examination which have been detailed can ever be improved upon. Detection, or the most perfectly satisfactory proof of the non-existence of the poison, in all cases of inquiry, is now certain. Furnished with this unerring test, it may be said that in a country in which the inquest of the coroner is established, there can be no secret poisoning. And it may added, that if the knowledge of this test be universally disseminated there will probably be no attempts to commit this crime.

But valuable as this certain detection of the fact when committed is, the prevention of the mischief must be admitted to be still more so. The few precautions which our retail druggists make use of in their sale of poisons, are, no doubt, useful as far as they go, but they are notorious for their inefficiency. The following suggestions of MM. Chevallier and Boys de Loury, which these gentlemen lately submitted to the French Minister of Justice, with the humane intention of rendering the crime of poisoning less frequent, will, therefore, certainly deserve the attention of the learned corporations in this country, whose duty it is to watch over the interests of this branch of public safety ; and we are confident that many of the individuals who dispense these deadly articles* to their fellow-creatures will adopt some of the suggestions, without waiting for the compulsory statute of the Hall or College.

M. Chevallier and his colleague are of opinion that poisoning would be rendered less frequent if it were required, by authority, that all poisonous substances should have either taste or colour communicated to them, except in the few cases where it might absolutely destroy their use in the arts.

That the white arsenic intended for steeping of corn, should be mixed with aloes in powder, in the proportion of ten parts aloes to ninety arsenic.

That the arsenious acid used for external applications, by veterinary surgeons and farriers, and by others in their treatment of the itch, should be prepared in the same manner.

That the arsenious acid intended to poison rats, mice, &c., should be mixed with Prussian blue or soluble indigo, in the proportion of ninety parts acid to ten colouring-matter.

That the metallic arsenic in powder, sold for the destruction of flies, should be mixed with a tenth of its weight of soluble blue.

If these precautions were universally adopted, it is highly probable that these gentlemen are correct in thinking, “ that in numerous cases taste imparted to food in which poisonous substances had been mingled, would be sufficient to warn the intended victims, and save them from the danger to which they were exposed ; and that in other cases, colour so given might have a similar salutary effect.”

We are sure they will be appreciated | not suffer them on his premises, and who by, at least, one in the trade-we mean the has inscribed on his house in large chacautious druggist of Barnstaple, who will racters, “No OXALIC ACID SOLD HERE.

QUESTIONS FOR SOLUTION RELATING TO METEOROLOGY, HYDROGRAPHY, AND THE ART OF NAVIGATION,

By M. ARAGO.

(Continued from p. 333, vol. I. ]

THE Springs of Aix, in Provence, have suggested to me a plan of experiment, of which I think it proper to insert a notice, as very probably the physical conditions on which it is founded may be met with in other places.

The town of Aix, in Provence, possesses baths of thermal water, known under the name of the Baths of Sextius. They are surrounded by an edifice, the building of which was completed in 1705. The spring was formerly so copious, that in the last two months of that same year, it was amply sufficient for the service of upwards of 1000 bathers. It fully supplied nine jets of a fountain, and nine baths. From the year 1707 the water began to be less plentiful, and in a few months was so much diminished, that the establishment was wholly abandoned.

Other warm springs exist in the town,-at the Cours, in the Garden of the Jacobins, at the Monastery of St. Bartholomew, at La Triperie, Grioulet, the Hotel de la Selle d'Or, the Hotel des Princes, &c., and at the bottom of certain wells, such as that belonging to Sieur Boufillon (at the corner of the Rue des Marchands), and some tanners' pits. These different springs diminished like that of Sextius, and even more rapidly. Many of them, and, among others, those of the Jacobins, of St. Bartholo. mew, La Triperie, and Grioulet, dried up entirely.

During the period that this diminution of many of the springs of Aix, and the entire destruction of some of them, was going on, individuals began to turn to their private advantage some very copious springs, which they discovered by digging to a small depth in properties situated a little distance from the town, in the territory of Barret. The idea that these new waters were precisely the former waters of the town soon occurred to the minds of many persons; but the impossibility of decisively proving that such was the fact, for a long time prevented the authorities from interfering. At last, in 1721, during the dreadful plague that prevailed in Provence, Dr. Chicoineau of Montpellier, having thought it expedient to order baths for the persons detained in quarantine, Vauvenargues, the commandant of Aix, came to the following resolution: “As the warm baths of the town of Aix appear to us necessary to wash and purify the convalescent patients in quarantine, and the said baths have not sufficient water for this

purpose, on account of the quantity that has been withdrawn from the source by various proprietors near it, we order, for the good of the service, that steps be immediately taken to prevent this,” &c. &c. In virtue of this order, the consuls caused the holes dug in the district of Barret to be filled up, and, in twenty-two days after this operation, the waters of the Baths of Sextius were augmented three-fourths, and many springs which had become entirely dry, that of Grioulet for example, again began to flow.

In May 1722, Vauvenargues having been superseded, the dispossessed proprietors pierced, under ground, the works which had been constructed the year before, and immediately the warm springs of the town were seen to diminish, and even entirely dry up.

In July 1722 the breaches were filled up by the vigilance of the authorities, and the inhabitants of Aix saw the waters reappear. Things continued in this state for five years; but in 1727 the tenants of the mills of Barret clandestinely made a new opening in the dam constructed in 1722. The knowledge of this misdeed was only acquired by a falling off in the quantity of water. In order to terminate this obstinate contest between private interest and the general benefit, the town passed an act defining the property, and caused a stone pyramid to be erected upon it, in 1729.

To these details, which we have entered into in order to establish the fact, that the waters of the pyramid of Barret feed the warm springs of the town of Aix, we shall add, that M. Dauphin, locksmith, assured M. Robert, a physician of Marseilles, in 1812, that he witnessed an experiment which places the matter beyond a doubt: he stated, that lime having been mixed with the water in the basin of the pyramid, the springs of Cours and of Mennes became milky.

Under the pyramid of Barret, the basin which the water occupies is also of stone; it is about 11] feet long and upwards of 6 feet broad. In June 1812, M. Robert sent down two men to ascertain the temperature of the water; they found it 62:6° Fahr. At the same period, the baths of Sextius were at 84.2° Fahr.

It

appears, therefore, established, that the cold waters of Barret become, at least the greater part, the warm waters of Aix, by traversing the short space which separates these two points,—that is to say, a horizontal distance, estimated in the official memoirs from which we have given an extract, at about a thousand geometrical paces *.

It will be observed that we have employed the words the greater part, and they, in fact, indicate precisely the question which remains to be answered. If it could be proved that all the warm water of the baths of Sextius originated from the cold water of the basin of Barret,—that the phenomenon does not consist merely of an intermixture which may take place near the surface, between the water of Barret and that of an ordinary thermal spring nearer Aix,—and that in its passage the fluid does not become chemically charged with any foreign substance, the theory of thermal springs would have made a decided step in its progress. Every one would then be satisfied of their similarity to the sources of Artesian wells, the high temperature of which is evidently owing to the great depth from which they issue.

Without pretending to devise the best means of investigation which the survey of the places might suggest, I conceive that if permission were

I obtained to withdraw the waters of Barret, for a few days only, the principal question would be solved. From the time that the intermediate thermal spring between Barret and Aix should begin to flow to Sextius alone, there would be, simultaneously, a considerable diminution of the

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quantity of water, and a considerable increase in the temperature of the baths. A comparative chemical analysis of the respective waters, if performed with that scrupulous accuracy of which we have now many examples, would be very interesting. Nor should it be forgotten to repeat the experiment mentioned by the locksmith Dauphin, by employing lime, or bran, or some tinctorial matter, were it only for determining the velocity of the fluid in the subterranean passages which it traverses, in passing from Barret to Sextius.

The temporary turning-off of the waters of Barret, is the most decisive mode of obtaining the solution of that very ancient problem of physical geography to which thermal springs have given rise; but should this deviation be impossible, there still seems to be a method of attaining the object. The waters of Sextius are said to diminish in dry, and to increase in rainy, weather. It is very improbable that the increase and decrease should follow exactly and simultaneously the same relations in the cold, and nearly superficial, waters of Barret, and in those of the thermal spring nearer the town. If a mixture of these waters does take place, we ought, therefore, to expect, that great variations of temperature would be observed at Sextius.

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be seen, by this single instance, how much the authorities have erred in suppressing the office of Inspector of Thermal Waters, under the idea that nothing in that department remains to be discovered. I now add, in conclusion, that the data on which my plan of experiment is founded, have been derived from a manuscript memoir presented fifteen years ago to the Academy by M. Robert, which has not, in my opinion, met with the attention which it deserves.

MEAN HEIGHT OF THE BAROMETER.—A few years ago a positive denial would have been given to the assertion, that there is any permanent difference between the barometrical heights corresponding to different regions of the globe at the level of the sea. At present such differences are regarded as not only possible, but even probable. The officers of the

. Bonite ought therefore to preserve their barometers with the most scrupulous care in such excellent order, that all their observations, made in every port, may be compared. Notice should never fail to be made of the exact height of the cistern of the barometer above the level of the sea.

OF THE INFLUENCE OF DIFFERENT WINDS ON THE HEIGHTS OF THE BAROMETER.—As soon after the memorable discovery of Torricelli as meteorologists directed their attention to the observation of the barometer, they perceived that, in general, certain winds produced a rapid ascent of the mercurial column, while the opposite ones produced a contrary effect, in a manner as equally decided. The difficulty was, to determine the numerical value of these influences. It was necessary, in order to eliminate entirely all transient and accidental influences, and to obtain the true measure of permanent causes, to operate upon great numbers; it was necessary to obtain long series of good observations made in the same locality; it was necessary to group the winds according to their precise directions; and, finally, to separate effects purely thermometrical.

Burckhardt undertook this labour, availing himself of twenty-seven years of observations which Messier had made at Paris, from 1773 to

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1801. If we designate by the letter H. the mean height of the barometer at Paris, that is to say, the height determined by the average of all the observations, the means corresponding to the different winds, according to Burckhardt's calculations, will be as follows:

Eng. In
South
H. minus 3, 1 (1.23) North

H. plus 2, 0 (0.78) South-west

2,9 (1.11)
North-east

+ 2, 6 (1.03) West 0, 4 (0:16) East

+.1, (0:39) North-west plus 1, 3 (0:51) South-east

+ 0,8 (0-31) It will be seen, from the mere inspection of this table, that the direction of the wind occasions a variation in the state of the barometer at Paris of 3mm, 1 (1:23 Eng. in.) above the mean, and of 2mm, 6 (1.03 Eng. in.) below it, forming a total variation of 5mm, 7 (2.26 Eng. in.); and that the opposite winds, combined two by two, give a mean height which, in extreme cases, scarcely differs by half a millimetre (0.19 Eng. in.) from the mean of all the observations.

M. Bouvard has presented to the Academy the results of an investigation analogous to that of Burckhardt; it is founded on the observations of the barometer made at the Observatory of Paris from 1816 to 1831, and leads, in general, to the same conclusions. By assigning to the letter H. the signification which we gave it in the preceding table, we shall have the following barometrical heights, corresponding to the different directions of the winds:

Eng. In. South H. minus 3, 7 (1:46). (2944) | North H. plus 3, 2 (1.27). (2140) South-west

3, 0 (1:18) (2847) | North-east + 3, 2 (1.27). (1390) West 0, 8 (0-31). (3402) East

+ 1, 7 (0.67). (1248) North-west plus 2, 0 (0•78). (1533) | South-east minus 1, 7 0.67).( 890)

The daily observations at nine o'clock in the morning, at mid-day, and at three in the afternoon, have all concurred in the formation of these numbers. Almost exactly the same results will be obtained by employing only the maxima heights of nine o'clock, and the minima heights of three o'clock.

In this instance, as well as in the table of Burckhardt, half the sums of the heights corresponding to the opposite winds are nearly equal to H., that is to say, to the total mean. The highest mean effect of the wind is 6m, 9 (2-73 Eng. in.), which surpasses the result afforded by the observations of Messier by lm, 2 (0:47 Eng. in.)

Both these tables tend to establish a fact with which meteorologists cannot be too strongly impressed,—that in order to obtain in our climates the mean height of the barometer, it is indispensable to admit into the calculation an equal number of observations corresponding to winds of opposite directions.

The tables which we have just transcribed, suggest many scientific questions; they lead us to inquire in what manner this influence of winds on the atmospheric pressure, varies with the position of places, with their greater or less distance from the sea, with their latitude, &c. In the mean time, till data sufficiently numerous be obtained to enable us to attempt the solution of these various meteorological problems, I shall here present to the reader the results of two series of very accurate observations, which were communicated to the Academy by MM. Schuster and Gambart.

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