GENERAL B. TERRESTRIAL PHYSICS AND METEOROLOChiversity without warning, many people being drowned in the or crushed by falling buildings, and scarcely any property being saved. Another suburb shared a similar fate, but the inhabitants were fortunately able to escape with their lives. All along the course of the main river and its tributaries towns and villages were destroyed, some with hardly a vestige remaining, and the dead were numbered by thousands. These destructive outbreaks have of late become periodical at Toulouse, but none have ever left such desolation behind as this one. Now for the moral of this pitiable story, and for the sake of which we have reproduced it. One cause of this terrible calamity, it is very generally conceded, is to be sought for in the wholesale destruction of the forests of the surrounding country, which has been going on for years. Our contemporary Iron puts the case concisely in the following terms: The cause of this calamity is, no doubt, the three weeks' previous heavy and continuous rains, which fell over the whole range of the Pyrenees; the drainage of this rainfall having been accelerated by the stripping of the mountains and upland tracts of their natural clothing. We have on several occasions pointed out the way in which this excessive and unwise destruction of natural wood, among other and serious climatic evils, aggravates the effects of the rains which usually fall at the equinoctial periods, but are not confined to them. In the present case it appears that there has been a widespread destruction of timber in the district during the century, and thus the exceptional downfall, neither intercepted by the loosened earth and undergrowth, nor absorbed by vegetation, scarcely penetrates beneath the surface, but runs off as it falls, spreading desolation now, and occasioning drought later in the year. The latest estimate of the loss by these floods is 2000 lives in Toulouse alone, and about $75,000,000 worth of property. Twenty thousand persons likewise are estimated to have been rendered homeless and destitute, besides being deprived of the means of earning their bread. CHANGES IN THE LEVEL OF THE WATERS OF LAKE GENEVA. Professor Plantamour, of Geneva, has subjected to examination the observations made since 1838 on the heights of the water of Lake Geneva. These observations have been systematically and carefully made for forty years, and in all cases the bench marks to which the levels of the water are referred are points so well known that the entire series of observations can be considered as perfectly comparable among themselves, except in so far as a slight uncertainty attaches to a portion of the observations, due to an accident which occurred to the recording apparatus. After carefully correcting and reducing the whole series of observations to a uniform standard, it appears that the annual variation in the height of the lake is distinctly pronounced for each year of observation, but that the water returns to the same level at the same epoch of each year. The lake appears to have been lowest in December, 1857, and to have been highest in July, 1846; the entire range between these figures being only seven feet. It is, on the average, lowest on the 11th of February, and highest on the 7th of August. The connection between the accidental or extraordinary variations in the level of the lake, and the meteorological conditions, especially rain and melting snow, is fully examined; and it appears that the heat of the autumn is a very important factor in determining the volume of the waters of the Rhone, and consequently that of the lake. By means of a table giving the quantity of rainfall, and the temperature of the spring for each year as compared with the averages, Plantamour is able to explain away so large a portion of the ir regular annual variations of height of the water that the remaining discordances are remarkably small; while there are groups of positive discordances, which have suggested the propriety of comparing the heights of the lake, year by year, with each other, in order to deduce the secular variations, if any exist. He has, therefore, divided his series into periods of nine years each, from which grouping it is shown that the level of the maximum water has not varied in any progressive manner in the course of thirty-six years, and that the annual fluctuations depend upon the dryness or wetness, the cold and the warmth of the year. If, however, within each of these groups, we compare the levels of the water, we find that the heights at low water are larger in proportion as the rainfall diminishes, and a gradual increase in the level of low water is noted, which can not be explained by atmospheric circumstances. These changes, it is suggested, are probably due to the modifications that have taken place in the course of years in the hydraulic works, and the drainage of the neighborhood. There seems to be no trace of such a change as Mr. Dawson states that he has found in the levels of the Great Lakes of North America, according to whom these vary in a period of about eleven years, following closely the changes in the solar spots.-Mem. Soc. Phys. Geneva, 1874. THE ELECTRICAL CONDITION OF SPRING WATER. Messrs. Theury and Minnich state that they have employed a delicate galvanometer in making some experiments on the electricity of the warm springs in Baden and Switzerland. One of the platinum electrodes was plunged into the upper spring at Stadthof, and the other electrode into the little stream Limbat. As soon as the metallic connection was completed, the needle of the galvanometer moved violently, oscillating about 74°; then in proportion as the electrode was covered with bubbles of gas, and became polarized, the galvanometer needle descended to 72°, and even to 60°, ascending to 70° when the electrode was cleansed of bubbles with a brush. This experiment shows that the thermal water was very strongly electrized, the source of the water being negative. Again, placing two vases of water side by side, the first vase filled with spring water, taken immediately from the source and still quite warm, the second vase filled with cold water from the river, the platinum electrodes were introduced, and immediately the needle of the galvanometer indicated a current flowing from the cold to the warm vase; that is, in the same direction as the current of the spring, the warm spring water being electrized negatively. When the spring water had completely cooled, it was again heated with an alcohol lamp to a temperature of 47°, and the electrode immersed, but without observing any appreciable current in the galvanometer.-1 B, XV., 411. ON THE SECULAR DIMINUTION IN EUROPE OF SPRINGS, RIVERS, A memoir by Gustave Wex, published at Vienna in 1873, on the diminution of water in springs and rivers, and the in crease in the flood waters in cultivated lands, has lately been the subject of a report by the Vienna Academy of Science, from which it would appear that the diminution experienced in the course of the last few centuries in the average height of the water (especially the low waters) of the Rhine, the Elbe, and other rivers of Europe, is to be attributed to a diminution in the annual quantity of water available for the rivers, and taking account of the amount of evaporation, there still results a diminution in the amount of water supplied by springs and rainfalls. It appears to the commission probable that the influence of forests is perceptible on the annual rainfall, and especially on the distribution of the rain throughout the year, although direct observations do not yet suffice to determine the magnitude of this influence. Among the causes tending to this diminution of the water in the rivers, the commission enumerate, first, the extinction of the forests, which exerted a beneficial influence in maintaining and elevating humidity, in diminishing the extremes of temperature, and diminishing the evaporation, and in assisting to a more equable drainage of the precipitation. A second cause is found in the drying up of the lakes, ditches, and morasses, which also would have exerted an influence similar to that of the forests. Third, in the cultivation of extended areas of land, which cultivation demands the consumption of considerable quantities of water. Fourth, in the increase of population, although the effect of such increase can directly account for only a slight percentage of the entire diminution. Finally, the commission consider the suggestion of Salmann as worthy of consideration, according to whom water is being employed in the interior of the earth in the formation of minerals which contain that liquid in chemical combination. In view of these considerations, the commission recommend that the Austrian government institute such observations as will lead to a further knowledge on this subject, and especially take such steps as will prevent the further diminution of water from becoming a calamity to future generations. Ef forts will also be made to collect more complete data from the inhabited portions of the world; and especially is the hope expressed that the Viceroy of Egypt may cause tables and graphic representations to be made of the observations on the height of the water at the Nilometer at Cairo, where such observations have been regularly made for the past 3000 years. The actual diminution in the annual average height of the water, as deduced by Wex, is, for the different parts of the Rhine, from 6 to 60 inches during fifty years; for the Elbe, at Magdeburg, 17 inches; for the Oder, 17 inches; and for the Donau from 18 to 55 inches. Sitzungsbericht der Akademie der Wissensch., Vienna, LXIX., April 23, 1874. PHOTOGRAPHING THE WAVES. The various mathematical theories that have been, thus far, elaborated with reference to the movements of vessels upon the waves are only approximate. It is only by experience that we are able to determine to what degree of exactness these theories have arrived, and in order to verify them it is necessary to register the successive inclinations that a wave gives to a vessel. The photograph allows us to obtain the law of these inclinations. Let us suppose that a photographic apparatus, having its axis perpendicular to the diametral plane, be directed toward some point in the hori zon. We should obtain on the sensitive plate an image of the sea and of the heavens, separated by a horizontal line, which would be the image of the horizon. Let us mark upon the plate the position of this image when the axis of the apparatus is upright. If it is then inclined by an angle, i, about a horizontal axis parallel to the diametral plane, the image of the horizon will remain parallel to the primitive line, but be displaced by a quantity equal to f, tang. i; ƒ being the focal distance of the objective. Let us suppose now that we place before the sensitive plate a fixed shutter pierced with a vertical slip; the image will be intercepted, except in that part of the plate situated behind the slip. We shall thus have upon the plate a broad band of two different tints corresponding to the sky and the sea, divided by a segment of the horizontal line. Consequently, if we take an instantaneous photograph at the moment when the ship is inclined at the angle i, we shall have a segment of the horizon line, and the distance of this line from the primitive horizontal line will give the angle i. In order to realize these conditions, it suffices to make the sensitive plate move horizontally with a uniform movement. If, during this movement, the |