evident that the simultaneous action of the two rulers and the plummets will show the three angles sought, and that nothing remains but to reduce, by calculation, the angle BAC to the plane of the horizon.

This instrument, arranged in the manner here de scribed, produced every desired effect in our experiments. The invention, as simple as it is happy, may become very important from the useful application of which it is susceptible; and there is already reason to hope that, by bringing this to perfection, or by the formation of some analogous instrument hereafter, there will be a possibility of executing trigonometric operations with much correctness, by the assistance of aërostatic machines, notwithstanding their continual motion.

It was not enough to have discovered the means of connecting the angles with the plane of the horizon: it was still desirable, that all the angles observed during ascents in any one place should have a relation to the common centre of observation. To accomplish this, it was necessary to keep a register, by some means, of the situation of the machine at the precise moment of measuring each of these angles. This was done by dropping from the aërostat, at that instant, a small stake, leaded, and furnished with an iron point. This stake fell rapidly to the earth, into which it stuck, and marked a point corresponding to the summit of the angle measured. It was then easy to compare the position of this point with that of one taken for the common centre of the observation, and thence to deduce the necessary corrections. It must however be noticed, that the stake, when abandoned to itself, acquires, at the instant of its fall, a compound motion, which partakes of that of the acrostat, and consequently is not exactly vertical; but the error which results from this deviation is but slightly perceptible in practice.

The

The calculations and ordinary processes of descriptive geometry will furnish all the means of making use of these different observations, and of expressing the results on paper; not only for their application to the construction of maps, but also to ascertain heights compared with the level: but we shall not in this place enter into any details on that head.

The observer engaged making these first experiments, soon perceives that the involuntary embarrassment, occasioned by the novelty of his situation, when he finds himself insulated and suspended at a height of seven or eight hundred metres, has a considerable influence both on the fidelity of his observations and on the time necessary for making them. All certainty depends, in fact, upon the confidence and readiness of the observer; and it cannot be concealed, that it may produce great inconveniences, because this difficulty of operating opens wide limits for ́the errors which it is possible to commit.

From this last observation it will be seen: first, that it is indispensably necessary to have acquired a great aptitude for these sort of observations, to be, able to execute them with precision: second, that the processes just described are more satisfactory in theory than they would be in those applications which require strict accuracy; and that, though there are situations in which nothing can be substituted for their use in the construction of some figured plans, it is at least proper never to use them in preference to those means of observation which are. better known, and which can be employed with more certainty.

But it cannot be too often repeated, at the same time, that aërostats furnish the means of giving the most lively interest to the delineation of the figure of the earth, in

maps

maps of all descriptions; and that their use is of the greatest assistance in the formation of plans, the outline of which may be sufficiently defined by a simple eyesketch. The aërial observer, by discovering a vast extent of country, accustoms himself fully to consider the general organisation of the asperities of the country, and even the particulars of its varieties, as well as the tone of colour, which appear to give a different character to each portion of territory. If this new method of observation be cultivated with assiduity, it will doubtless lead to a sensible improvement in the art of drawing plans. But to benefit by the advantages which it affords, it is necessary that those who are destined to this employment should join a profound knowledge of geometry to a great facility in designing landscapes. May they be convinced of the importance of this truth, and assure themselves that no part of the plan can arrive at perfection, either ornamental, or relative to civil and military purposes, unless strict accuracy in the outline is accompanied by that fidelity of expression which is capable of producing in those who inspect the plans, all the ideas which the observer had formed from the aspect of the country.

From all that has been said, we may conclude, that the aerostatic art combines properties no less valuable than unquestionable in topographic operations and military researches; that its perfection may produce new and invaluable properties; and that it would be equally impolitic to neglect the use of these machines, or not to obtain for them the information to be derived from reflection and experience. We shall terminate this memoir by an observation relative to their military uses. Our enemies would not fail to oppose to the creative industry of France, an industry of imitation: they would also have

their balloons and ballooners. The influence of this innovation in war is of a nature to spread with rapidity, and it must soon cease to favour any nation exclusively. But even in this case the art of aërostatic machines will have acquired a higher degree of interest, because another element will then be in the power of man, in which the efforts of genius and industry may be substituted instead of the inconsiderable devastations of force; and this observation ought to interest the friends of humanity in bringing them to perfection.

Method of procuring very strong Vinegar at a trifling Expense.

From the BIBLIOTHEQUE PHYSICO-ECONOMIQUE.

THE

HE manufacture of oiled cloths consumes a great quantity of vinegar. The acetite of iron (solution of iron in vinegar) is the material employed in the colouring to obtain from madder all the red-browns and the various shades of violet. These colours are the more brilliant and vivid according to the superior quality of the acid employed.

The vinegar of the shops varies ad infinitum both in price and quality; it would therefore be highly advantageous to the manufacturer to prepare himself a vinegar of a good quality, and always of equal strength. The following process promises this advantage. It is extracted from a theoretical and practical course of lectures on painting, held at Berlin, under the auspices of govern ment by that able chemist professor Westrumb.

Take twenty pounds of unripe grapes, together with the stalks; bruise them in a mortar, and put them into a hogshead holding 68 gallons or 272 quarts.

In a boiler of copper, or preferably of tin, boil 150 quarts of river water with four pounds of red tartar. When the tartar is dissolved, add six pounds of common treacle. Pour the whole over your grapes, and lower the temperature by the addition of fifty quarts of cold water and two quarts of yeast. Observe that the vessel be filled only to about an inch below the bung - hole. After having well mixed the composition, remove it to a place where a regular heat of twenty to twenty-five degrees of Reaumur is maintained.

The fermentation takes place in the course of a few days, and continues sometimes for a month. When it has ceased, which may be known by the absence of the froth which covered the liquid and the vinous odour which succeeds the pungent smell it before exhaled; the bung-hole must be closed, and the vessel left perfectly quiet for a fortnight, that the liquor may become clear.

At the expiration of that time draw off the liquor by means of a cock; add eight quarts of brandy and six of common vinegar; place the vessel in a moderately warm situation, in summer under cover; let the liquor be six or seven inches lower than the bung-hole, which must be left open. A few weeks will be sufficient to convert it into very strong vinegar.

As soon as you find it of sufficient strength, remove it into another vessel, and keep it carefully bunged. The prime cost of the Berlin measure, weighing 24 pounds, is 8 to 10 pfennings, or about one penny of English money.