PHOTOGRAPHY.*

M. ARAGO wished to be heard, in order that he might make known some essential rectifications to the verbal communication which he had made on the preceding Monday, in reference to M. Daguerré. The inaccuracies committed by the secretary have been in consequence of explanations very little developed which had been given him, on the subject of new photographic processes. It is even to be feared, that the letter of M. Daguerré will not entirely satisfy philosophers, after the lively interest and curiosity which the results announced on Monday last would naturally excite. We will, however hasten to make them known: the facts remain the same as they previously were; the corrections of to-day do not remove any thing which they had appeared to offer of the marvellous, it being of no matter, in effect, whether the instantaneous action produced by the interposition of electricity is produced on this or that substance. M. Arago again adds, in order to excuse himself to those experimenters who since the announcement of Monday have vainly endeavoured to excite by the electrical spark the ioduret of silver; that neither he nor M. de Humboldt heard the word acidulée, when the ingenious artist imparted his new discoveries to them. We add a copy of M. Daguerré's letter to M. Arago :

"

My dear Sir, I have this instant received the Compte Rendu of the session of last Monday, and I perceive that an error has crept into the communication which you have there made of my new method.

"It is in speaking of the iodized plate. Though I do not think that the ioduret of silver is insensible to the electric fluid combined with the action of light, I have not as yet found any magnet, either direct or indirect, capable of forming the image with the vapour of mercury; for otherwise the process will be now as complete as the first, since the face of the plate so prepared is now so sensitive as not to allow time to open and shut the diaphragm before and after the electrical discharge.

"You will doubtless recollect that I spoke to you of a plate acidulée.

“As many persons have, without doubt, already tried to experiment upon my new method, by making use of a plate iodurée, submitted without any intermedial to the vapour of mercury, they will necessarily not have been able to obtain any thing. I trust, then, that you will be willing, as soon as possible, to destroy the word iodurée, which has led them into error. Besides, this communication ought not to be considered but as giving solely the invariable principle of the method.

"I feel so much the necessity of occupying myself in the most active manner possible on these experiments, that I quit all my works in order to give myself entirely up to them.

• Compte Rendu.

I thank you a thousand times, my dear Sir, for all the trouble that I give you, and I pray you to accept my lively gratitude.

"Bry-sar-Maine, 5th July, 1841.”

DAGUERRE."

THE ARTESIAN WELL OF GRENOBLE.*

Ar Grenoble, in the vicinity of the French capital, it was considered advisable some years ago to endeavour to procure good water by means of an Artesian well. M. Mulot d'Epinay was the engineer to whom the task was entrusted. On the 31st of December, 1836, the bore had been carried, after immense labour, to the depth of 383 metres (a metre is 3 feet and 2-10ths English). The soil was a clay, very hard and compact. In the month of June, 1839, the bore had reached the depth of 466 metres, and the soil was still a bed of clay, though a variety of strata had been previously passed. M. Mulot kept a regular journal of observations, relative to the soils and strata penetrated, and the temperature at different depths. This record will be valuable when published. At length, after a task of seven years one month and twenty-six days' duration, M. Mulot was rewarded by a degree of success proportioned to the time and trouble expended. Water was not only found, but found under such circumstances, and in such quantities, as will cause the well to be one of the most useful works, as well as one of the greatest marvels of artistical ingenuity in France. The fluid burst out in a perfect torrent, rising to the surface of the bore to the amount of nearly three cubic metres in a minute, or 180 metres in an hour, and 4320 metres in the twenty-four hours. Such is the force with which it flows up the shaft, that it mounts more than thirty-two English feet above the surface of the ground. M. Hemery, director of roads and bridges, has calculated that the force of ascension of the water, at the bottom of the shaft, exceeds, by fifty times, the force with which water rises in a vacuated tube of thirty-three feet. The orifice of the well is fifty-five centimetres (about one foot eight inches) in diameter, and at the bottom it is eighteen centimetres in diameter. The shaft is in all 547 metres (or 1630 French feet) in depth, and the sides are strongly plated with iron to a depth of 539 metres. The dome of the Invalids, which has an elevation of 300 feet above the ground, is thus only about a fifth of the perpendicular measurement of the Artesian well of Grenoble.

Three times, during the operations, did the shaft give way, but the indefatigable engineer was not daunted, and at last he has had his reward. The water, which the well pours forth incessantly, has converted one of the neighbouring streets into a river, but the workmen are at present employed in forming a channel for its proper con

veyance from the spot. As might be expected, the fluid was at first mixed with sand and earth, and continued to be so for some time. It is perfectly sweet, however, and had no odour of a disagreeable kind, or any other deteriorating qualities. It is of such a temperature that there is an obvious smoke arising from it when it reaches the surface. This is a feature not likely to continue, and indeed easily removable before use. The whole cost of this great work of art to the city of Paris is said to have been 160,000 francs. The perseverance in this labour for such a period of deferred success, is to be ascribed to the confidence resulting from modern geological discoveries; and the value of these is most splendidly shown by the success attained. By an ingenious contrivance, M. Mulot has been able to raise large quantities of sand from the bottom of the well; thus clearing the water more rapidly, and also adding very considerably to its force and volume. This removal of the sand has been attended with curious consequences in more respects than one. After ceasing, in a great measure, to throw up sand, the well has begun to throw up shells and petrifactions of various kinds, the debris of a former world. The success of the operations of Grenoble has also induced engineers to make similar attempts in other quarters. One is begun on a large scale at Vienna.

WHIRLWIND IN LIVERPOOL.-On Thursday, May 11, at halfpast three o'clock in the afternoon, the inhabitants of Bond-street and the lower part of Burlington-street, were thrown into a complete state of excitement and amusement by the occurrence of a whirlwind. The empty space of ground between the two streets is a hollow, of about twenty feet in depth, and is much used by the inhabitants for drying clothes, for which purpose posts are fixed in the ground at convenient distances, to which lines are attached. At the time above-mentioned, the hollow was completely filled with clothes, drying upon the lines; for some time previous there was not a breath of air, when all of a sudden it began to blow very hard, and what appeared strange was, one part of the clothes streaming out in one direction, and another part the contrary way. In a short time the currents met, and the lines were almost instantly stripped; some articles of clothing were carried in a straight line upwards to an altitude of about 500 feet, when they seemed to have got into a different current from that of the smoke of the neighbouring chimneys, the latter blowing southward, while the clothes were carried away in a northerly direction, and they have never since been heard of, at least, by the owner.

ELEMENTARY LECTURES ON ELECTRICITY, &c.

LECTURE XVII.

IN persuing our illustrations on the electro-mechanical agency in the production of certain effects, it may not be amiss to employ different kinds of bodies in the circuit, in order to show how they are differently affected by modifying the mechanical action in the discharges of similar quantities of the electric fluid upon them.

I will, for instance, place a small loose ball of tow between the balls of the universal discharger, and discharge upon it a large Leyden jar, from a high degree of intensity. You observe that the tow, although an inflammable body, is not ignited; but several of its fibres are broken, and it is somewhat flattened by the mechanical action of the discharge.

Now, although the tow has escaped conflagration in this case, it does not always remain unignited by operating upon it in this manner. Its ignition, however, is very much facilitated by scattering some finely powdered rosin amongst its fibres, as you will presently see, by sending a discharge of a similar quantity of electric fluid through it.

Now, in order to convince you that the ignition of the tow and rosin is a general result of this mode of operating, I will repeat the experiment a few times, and you will then have ocular demonstration of the fact.

If, instead of rosin, I sprinkle the tow with oil of turpentine so as make it somewhat moist, you will see by a few experiments that the ignition is as easily and as regularly accomplished as by the employment of the rosin. We occasionally employ other inflammable matter amongst the fibres of the tow, for purposes of this kind; and when tow is not at hand, other fibrous matter, such as cotton wool, is resorted to, but sheeps' wool is seldom, if ever, employed.

In all these experiments you will have observed, that a considerable report attended each discharge of the jar, which, as I have before shown you, can take place under no other circumstance than when the velocity of the electric fluid is very great; for if we abate the velocity, by passing the fluid through an inferior conductor, the wet string, for instance, scarcely an audible noise attends the discharge. But for fear of taking too much upon credit, I will vary the experiment in different ways, and I think the results in every case will serve as so many facts, in the direct process of demonstration.

In the first variation of the experiment I will again place a ball of tow, sprinkled with oil of turpentine, between the balls of the universal discharger; and in another part of the circuit I will place another ball of tow, sprinkled with powdered rosin, between two other insulated balls. Between the inside of the jar and the first portion of tow, I place in the circuit a piece of tinfoil, between a few leaves of writing paper; and on the other side of the latter ball of