but still a great rain for that day. The classing of the rain might have been extended further, into very great rains, or so; but no advantage could be derived from such an arrangement, as will appear from the rules obtained from this article, which will be found most wonderfully consistent and regular. It is to be observed of showers, that when these are frequent, they make up a moderate rain, and even on rare occasions a great rain, but very generally only a short rain; the time and the effect in these cases are considered.

"The method of finding the sum of rain in a season is this: Taking an extreme case for an example, winter 1804-5, it had 5 great rains, 12 moderate, and 25 short rains; the great rains are each supposed equal to 6 short, and the moderate to 3 short rains; and these being added to the actual number of short rains, the whole sum is 91 short rains; but as this number has been considered an inconvenient one, particularly as it would require in general three figures, it is divided by 4 on all occasions, which reduces the product to two figures, at least by the seasons, which was the first mode of treatment of the subject adopted, the System by years having been found long after; therefore, 91 being divided by 4, the quotient is 22; but as no fractions are admitted in the sum of rain for a season, the sum total is called 23 for this winter. Any other mode would have served as well, if continued throughout, but this appeared the simplest, and the result has fully warranted its continuance, and for the reason stated, as to the rules obtained in consequence of this arrangement, it giving an exceeding correct result; moreover, it was absolutely necessary to find a round sum, as the representa tive of the variety of the rain which falls in a season, which has the advantage of simplifying the subject, so as to be easily under

stood and recollected.

As

"In estimating the sum of rain-snow, hail, and sleet, are always included. an enumeration is made of the days' snow in a season, it is explained thus: Any day upon which snow falls, is termed a snowy day, though probably a greater proportion of the fall may have been in rain: this distinction has been made, merely to shew the prevalence of snow upon any season: thus it will be seen that the second winter observed, that of 1803-4, though a

mild winter, yet there was an extraordinary quantity of snow as well as of rain.

:

"The sum of the force of the wind is found much in the same manner as the rain Thus, there are gales, and high winds, and windy days; but the high winds are classed under gales, and each supposed equal to 6 windy days, and the sum thus found are added to the actual number of windy days in a season; the whole then is divided by 4, which is a common divisor, and the quotient represents the sum of the force of the wind for the year. It happens, however, on rare occasions, that the gales and high winds

are of short continuance, though frequent, in which case less value is attached to these of course, and are multiplied by 4 or 5, instead of 6, according to circumstances; the first instance of this kind is in the winter and year 1815-16, and also in 1816-17,

"In estimating the quantity of frost in a season, the days or nights on which this phenomenon appeared, are termed a day of frost, and the number of these in a season are simply the number of the frost. A more accurate comparative sum might have been obtained, by a clasification similar to the rain, viz. hard frost, moderate frost, and slight frost, which might gratify the curious; but there was labour enough without this addition.

Of the other phenomena of weather, viz. thunder, lightning, aurora boreales, &c. it has been only necessary to note them in the order of appearance, giving the sums of each at the end of the season or year, as will be found in the tables in the history of the wea ther; only remarking here, that however frequent the thunder or lightning is on any day, it counts but as one day with thunder, &c.

By observing the number of days of east and west wind for 14 years, Mr Mackenzie found, that the average number of days of east wind was 135, and the average number of days of west wind 216, a ratio which, for reasons afterwards to be mentioned, he considers as approaching to that of 140 to 210, or 2 to 3. If the east wind, on any given year, shall amount to more than the average of 135 days, there is then an excess of so many days of east wind, but if it amounts to less than 135, there is then a deficiency of so many days of east wind. The same is done with the west wind; and the excesses or deficiencies of both winds are put down for each year. the phenomena of the weather can have no relation to our civil year, Mr Mackenzie begins the weather year, as he calls it, upon the 1st of November, because it is at or near this period that there is the most material change of weather during the whole year, and that this is the only day which gives

the

As

averages leading to the system, or rather, it comes out strongest on this day, gradually becoming weaker before and after, till it disappears altogether on the 26th October and the 5th November. Having in this manner found the exces winds for 14 years, he began to comses and deficiencies of the east and west pare them together, and was surprised to find, that they followed one another in a regular progression, the excesses and deficiencies of both winds arrang◄

ing themselves in groups. The natúre of this progression will be understood from the annexed table, consisting of three columns. The first column contains the Years of Observation, the first of which commenced in 1802-3, or on the 1st November 1802. The second column contains the Excesses and Deficiencies of the west wind, and the third the Excesses and Deficiencies of the east wind. Upon comparing these E's and D's, it appears, that in the east wind column the Excesses are grouped in the following manner, EEE, EE, E, and the Deficiencies, which are interposed between them in the following manner, viz. D, DD, DDD, DDDD. In the west wind column the progression is E, EEEE, EEE, EE, and DD, D, DDD. Now it is a very remarkable fact, that by following out these progressions the series returns into itself in 54 years, forming a perfect cycle.*

FORM OF THE SYSTEM.

In the preceding scale, the number of the series of excesses and deficiencies of both winds is exactly equal, viz. 24 groups of each; but if we reckon them individually, we shall find, that the excesses east are 24, and the excesses west 30; and that the deficiencies east are 30, while the deficiencies west are only 24. Hence the east wind is one-fourth less in excess, and one-fourth more in deficiency than the west; that is, it blows one-half less frequently than the west, or the two winds are to one another as 2 to 3, a result which harmonizes in a very sin◄ gular manner with the ratio of 135 to 216, deduced by Mr Mackenzie from 14 years' observation.

Although it is absolutely necessary, from the nature of the cycle, that the excesses and deficiencies of the east and west wind shall return every 54 years; yet it by no means follows, that the weather in any one cycle shall in every respect resemble the weather in any other cycle. The time of excess and deficiency of both winds may be constantly varying, and may be performing another periodical change of greater or less extent.

"It must therefore become desirable," says Mr Mackenzie," to ascertain how far one revolution of the system of the weather corresponds with another in every particular; and if journals, conducted upon a sufficiently circumstantial plan, can be found, something of a solution of this point may be accomplished."

We have thus endeavoured to give our readers some notion of the general system delivered by Mr Mackenzie. This, however, forms a very small portion of his work, which contains also Particular Rules of the Weather, deduced from observation; the History of the Weather from 1802; the Laws of the Wind; and the Distribution of the annual series of the Wind upon the seasons. As it is in the power of every person to examine, by their own experience, the accuracy of the rules for the weather, we shall lay before our readers some of the most import

ant.

4. When there are two seasons together, either summer or winter, something considerably under average, the succeeding is average; and the season following, which is the fourth, respectively, is very wet; and the next, or the fifth, is very dry, but not always an extreme dry; for an extreme dry is only to be expected when the extreme wet is suddenly brought about.

5. Two average summers together are followed by a very dry one in the next year, and this by a very wet one, which is succeeded by a dry one.

6. When two wet winters, or two wet summers, come together, neither are ever in extreme.

7. When a winter and a summer are wet in succession, the succeeding winter is dry; and when a summer and a winter are wet in succession, the next summer is a dry one.

8. When a summer and a winter are average in succession, the next summer is either wet or dry.

9. No three seasons together in succession, or respectively, are ever wet average, or dry.

10. No three seasons whatever, taken in succession, or respectively, have ever more rain above average, collectively, than is to be found in one season of extreme wet, and vice versa.

11. After every course of wet, there is a course of dry, however short or long either may be, and vice versa.

12. A mild winter is followed by a mild summer.

13. A wet summer is always followed by a frosty winter.

14. Every frosty winter is in general followed by a cold summer.

15. An excess of west wind in win

ter is followed by much thunder in the following summer, provided the excess west be preceded or followed by excess east in the summer, and if both happen, the thunder is still more considerable.

16. A deficiency of west wind in winter greatly diminishes the thunder in summer.

17. An excess of east wind in summer is followed by thunder in the winter, and there is never thunder in winter but after an excess of east wind in

summer.

It would be impossible to give any explanation of the other portions of Mr Mackenzie's work, particularly the

very curious part of it relative to the distribution of the wind upon the seasons, without entering into tedious details; and we must therefore content ourselves with recommending the careful perusal of his book to all those who are interested in the very important subject of which it treats. Diligent and careful observation is the only test by which the system can be tried. Upon this foundation the author rests it; and he is therefore entitled to have it candidly and carefully examined.

A DESCRIPTION OF THE VAL DE BAGNE, IN THE BAS VALAIS, AND OF THE DISASTER WHICH BEFEL IT IN JUNE 1818.*

[We are indebted for the following interesting article to our friend Professor Pictet of Geneva, who has had the goodness to send it to us, previous to its appearance in his own excellent Journal, the Bibliotheque Universelle.]

THE Val de Bagne is a transverse valValais: it cuts, almost at right angles, ley in the high southern chain of the many other smaller chains, forming part of the great mass of mountains which separates Switzerland from Piedmont, At every point where the valley of Bagne intersects these different chains, it is rendered extremely narrow. In many of these gorges, the Dranse, which occupies the bottom, is the pick, leaving only a very narrow confined in a rocky channel cut with bed, from whence it passes into more extensive basons formed in the lower part of the valley, and which, before the late melancholy event, presented level plains, covered with the

*This interesting account contains a detailed report of what was verbally related, on the 29th of last month, to the Helvetic Society of Natural Science, at Lausanne, by Mr Escher de la Linth, who was witness to the disasters he describes. He illustrated his relation by a model of the valley, formed of clay jointly by him and Mr Venetz, an engineer of the Valais, who was of eminent service in very critical circumstances. This model, which spoke to the eye while the reporter addressed the judgment and the feelings, rendered quite luminous all those details which the imagination can present to us but imperfectly without such assistance.

PICTET

richest verdure, and studded with beautiful groups of houses and barns, shaded by lofty trees.

The southern chain of the valley, setting out from the separation of the Val de Bagne from the valley of Entremont, which leads to the Hospice of St Bernard, rises very soon to the elevation of perpetual snow, and forms the most northerly point of the icy peaks of Mount Combin. The northern chain does not rise so abruptly, and only reaches the line of perpetual snow at Mount Pleureur, situated six miles distant from the entrance of the valley. Thus far this chain separates the Val de Bagne from the great valley of the Rhone; but, at that point where it rises to the line of perpetual congelation, it takes a southerly direction, and then separates the Val de Bagne from the valley of Hyères, which, like the former, is a lateral branch of the great valley of the Rhone. Mount Pleureur de scends very rapidly into the valley of Bagne, and there forms with Mount Mauvoisin, which rises opposite to it, a pretty long gorge, in which the Dranse is confined in a channel of from twenty to forty feet in breadth, and whose sides shoot up vertically to the height of about a hundred feet, so that the bridge of Mauvoisin, which connects the two sides of the valley, rests upon perpendicular rocks eighty feet above the bed of the river.

By the side of Mount Pleureur, towards the bottom of the valley, rises Mount Gétro, whose steep sides, formed into steps by the strata of the rocks composing the mountain, and having but little inclination, are in some parts covered with pasturage, where there are many chalets in very lofty situations. A very narrow and pretty deep channel separates Mount Gétro from Mount Pleureur. The glacier of Gétro is situated at the top of it, and forms the most advanced point, towards the north, of that great uninterrupted range of glaciers which, from the Great St Bernard, as far as the Simplon, crown the vast chain of the Alps which divides Switzerland from Piedmont.

At all seasons, the water of the glacier of Gétro falls in cascades into the ravine, which descends with a very rapid fall into the Dranse, at the upper end of that gorge in the valley where the bridge of Mauvoisin is situated.

For some years back, however, the glacier of Gétro has advanced so far upon the ridge of the rocks which form the upper side of this extensive channel, that enormous masses of ice are constantly falling into it from the glacier above, and are swept over by the waters of the cascade with a tremendous crash, Part of them are caught upon the steep ledges of the rocks of the gorge; the remainder falls down into the bottom of the valley, where these fragments accumulate more or less, according to the quantity of ice which the glacier furnishes, and the season accelerates or retards the melting of them.

It is now five years since the accumulation of these blocks of ice, falling from the edge of the glacier of Gétro into the bed of the Dranse, began to form a new glacier in the shape of a half cone, whose summit is in the ravine, about a hundred feet above the bed of the river, and whose base so completely fills up this part (always a narrow one) of the Val de Bagne, that the side of this icy cone, inclined to about forty-five degrees, leans, to the extent of two hundred feet, against the almost perpendicular base of Mount Mauvoisin, which is opposite to the glacier of Gétro, in the chain on your right hand as you ascend the valley of Bagne.

This new glacier, which thus absolutely closes up the bottom of the valley, is certainly not exclusively composed of fragments of ice fallen from the top of the glacier of Gétro: avalanches of snow seem to have had a part in the formation of it; and after this collection of ice and snow became once thick enough to resist the transient heat of the preceding summer, it is clear that the snow of the following winter, added to the new avalanches of ice and snow collected in this fatal ravine, was more than sufficient to enlarge the new glacier, which, by means of rain water and melted snow filtering into it and freezing anew, composed at last a homogeneous mass of ice, of so enormous a bulk, that the period of its destruction cannot be calculated.

In the meanwhile, the waters of the Dranse, which are supplied by the glacier of Tzermotane and some others at the head of the valley, and which already form a pretty large torrent, still

found an outlet under the glacier, the base of which was doubtless thawed by the heat of the earth, and that of the water passing under it. Already, in the course of last year, the river had been obstructed by the glacier for a considerable time; but it suddenly opened for itself a passage, which did considerable damage in the lower part of the valley, even as far as Martigny. It was in the month of April last, however, that the waters of the Dranse were observed to be dammed up in the bottom of the Valley of Bagne, forming a lake of half a league in length. The danger of a sudden efflux of the lake, the surface of which was rising and extending every day, was too imminent not to lead to the adoption of every possible means to prevent such a disaster. It was resolved to cut a subterraneous gallery through this enormous cone of ice, sixty feet lower than the line of contact of the new glacier with the side of Mount Mauvoisin, a level at which the new lake, which was always increasing, would necessarily pour itself into the lower part of the valley, if the opposing glacier could resist the enormous pressure of the mass of water accumulated above it.The point at which the draining gallery was carried through the glacier, was fixed at the elevation which the lake was expected to reach at the period of its completion. It was expected that, in consequence of this artificial outlet, the water, in passing through it, would gradually furrow the bottom, and, of course, lower it, while the surface of the lake, by that means, would subside in the same proportion, thus daily diminishing the risk of the rupture of the glacier, and the sudden efflux of the water which it retained. This operation, which was admirably calculated to obviate the impending danger, was executed under the direction of Mr Venetz, an engineer of the Valais, with unshaken perseverance and courage, in spite of the difficulties which every day presented themselves, and the danger of working in a place where blocks of ice were constantly falling from the upper glacier, and in a mass which was liable at every instant to be undermined by the lake, or rent in pieces and carried off by the enormous pressure of the water. This perilous undertaking was begun on the 10th of May, and VOL. IV.

finished on the 13th of June. During these thirty-four days the lake rose sixty-two feet; but during eight days, the increase of its waters having, on account of the falling of the temperature of the atmosphere, only raised the level four feet, the upper entrance of the gallery was still many feet above the level of the lake; and the intrepid Mr Venetz had thus time to sink the floor of that opening several feet, in order to accelerate the efflux of the lake, and thereby diminish the mass of water which was indefinitely accumulating.

During the dangerous working of this gallery, extending to 608 feet in length, through the thickness of the glacier, masses of ice, of many thousand cubic feet, were detached from the base of the glacier on the side of the lake. The fragments, after falling into it with a crash, ascended to the surface, forming small floating ice islands. These accidents shewed the risk which the workmen in the gallery ran, at every instant, of being crushed to pieces and buried under the glacier.

On the evening of the 13th of June, at the moment when the water began to issue from the gallery, now happily finished without any serious accident, the lake was from ten to twelve thousand feet long; its medium breadth, at the surface, might be seven hundred feet, and at the bottom one hundred feet. Thus its absolute medium breadth was four hundred feet, and its absolute medium depth two hundred. The lake, therefore, contained, at the period of its greatest height, at least eight hundred millions of cubic feet.

From the evening of the 13th of June, to the 14th at eleven o'clock in the forenoon, the lake still continued to rise a little, notwithstanding the outlet by the gallery. After this period the bottom of the gallery began to wear down, owing to the melting of the ice over which the water flowed; and by five o'clock of the evening of the same day the lake had descended a foot. On the 15th of June, at six o'clock in the morning, the floor of the gallery was so much lowered, that the height of the lake was diminished ten feet, and twenty-four hours after was less by thirty feet. On the 16th of June, at six o'clock in the evening, being the moment at which

M