burg being a woody country, but also because it is exposed to the cold east wind. The translator points out the difference of height, which in the original is unattended to.

The author shows from historical comparisons, that the clearing away of woods makes the temperature of countries warmer. Whether the proofs that he adduces for this purpose are all quite convincing, we cannot positively affirm, though the fact itself is true; for France is no more deprived of its woods than England. If, then, there be, at present, nearly the same degree of heat in London and Paris, while, in the time of Tacitus, Gaul must have been colder, it is not quite clear why this contrary influence should proceed from the same cause. But it is also doubtful whether Tacitus would not, even now, if he had no assistance from the thermometer, call London milder than Paris, because severe winters occur less often in the former than in the latter city. But though the details of these comparisons may occasionally be uncertain, and more particularly those which relate to the question, whether a difference of temperature in former times ought to be attributed solely to the great abundance of woods and forests, yet a collection of the accounts of a greater degree of cold having heretofore existed, is doubtless very important. There can be but few to whom it will not be interesting to learn how much the cold of winter, especially in the south of Europe, has diminished.

CHAP. II.-Influence on the quantity of Rain.

The author here brings forward some observations to prove that more rain falls on the sea coast than in inland districts, and that, moreover, when chains of mountains run parallel to the sea-shore, the sides next the sea receive more rain than their opposite sides. In reference to woods, however, the author supposes that he may lay it down as a fact confirmed by observation, that woodlands in flat countries do not perceptibly increase the quantity of rain; but that woods on mountains have a perceptible influence in producing that effect. He thereupon founds the conclusion, that if mountains are planted with trees, the quantity of rain in their vicinity will be increased, and that the progressive diminution of rain in the south of Europe is to be ascribed to the destruction of the mountain woods. But the author does not appear to have been sufficiently careful in ascertaining what are the places in which the rain has diminished. It has not diminished in all parts of the south of Europe; for Flaugergues has found that the quantity of rain has considerably increased at Viviers, in the south of France, since 1778. The Milanese Ephemerides indicate the same thing for Milan, and all the assertions of this kind require further demonstration.

CHAP. III. Of the Influence of Woods on the Humidity of the

Atmosphere.

Here the author describes, among other things, an interesting experiment with the hygrometer, according to which the humidity of the air in the West Indies is found to be expressed by the numbers

3, 4, and 15, according as the observations are made on the coast in the midst of cultivated plantations, on the borders of mountain woods, or in the midst of those woods. There seems, however, to be some obscurity in an observation which the author is induced to make, namely, that the humidity of woods in the torrid zone extends far above the extremity of the scale. Now, as the hygrometer is usually graduated up to the point of complete humidity of the atmosphere, it can only be said that the moisture is precipitated in greater abundance than is necessary to bring the hygrometer to the highest degree.

We cannot venture to quote any more of these observations, or to explain the grounds of the doubts to which the conclusions drawn by the author give rise. But notwithstanding these doubts, we confess with pleasure that much information is to be found in the work. At the same time, we must regret that the translator has not given to his version that great superiority over the original which it would have obtained had he subjected several of the author's statements, such as those relative to the comparative humidity of the Mark of Brandenburg and Holland, to critical investigation.

CHAP. IV.-Influence of Woods on Springs and Running Water. That countries, especially mountainous countries, which are covered with woods, also abound more in waters than others, is a fact which may be asserted with little fear of contradiction.

CHAP. V. Of the Influence of Woods on the Wind and on the State of the Atmosphere with respect to Health.

Though many remarks which occur in this chapter are just, we are much surprised at some of the assertions, and we think we do not err in considering them unfounded. Among these is the assertion, that the impetuosity of the winds, where there are no woods to mitigate its violence, has rendered a great part of Great Britain barren. If the author's estimate, that the waste lands amount to 2 of the whole surface of Great Britain be true, it does not follow that these lands are barren in consequence of a deficiency of trees. The heaths in the north of Germany, which are not all situated in places entirely destitute of woods, show clearly enough that circumstances, which accompany an effect, are not always those which produce it.

The comparison between that part of Tartary inhabited by the Calmucks and Lombardy, appears to be equally unfounded. Whoever, in this instance, though the geographical latitude should be the same, expects to find the climate in both regions alike, and ascribes the dissimilarity of the climate to the want of trees in Tartary, must certainly have allowed many circumstances, which ought to have been taken into account, to pass unnoticed.

CHAP. VI.-Influence of Woods on the Fertility of the Soil. We also meet with many remarkable observations and important conclusions in this chapter. But upon the whole, we think that this

essay must be considered as a work which has not been reflected upon with sufficient deliberation. Nevertheless, it contains an abundant collection of curious facts; and though some of these facts are not well applied, and the accuracy of others remains to be proved, the book will, in the mean time, be found an excellent contribution towards the explanation of the subjects of which it treats.

There are, occasionally, some obscurities in the reasoning; but whether these ought to be attributed to the author or the translator, we have not at present the means of determining.

[Quarterly Journal.

Account of a new method of Filtering Water, invented by JAMES WHITE, ESQ. Engineer.

THE filtration of water in a mountainous country like Scotland, where water is in general pure, is comparatively a subject of less interest than in flat and fenny districts, or in great cities like London, which is supplied chiefly from the collected waters of the Thames. The means of purifying water under such circumstances, is a matter of the first importance to the health and comfort of the community.

It is well known, that, till of late years, the want of good water has been severely felt in the lower parts of Lincoln, Kent, and other fenny districts. In some of these, where the inhabitants and their cattle suffered much from the want of good water, the evil has lately been removed where this essential necessary of life has been supplied by means of perforations made to a great depth in the soil, by boring with an iron auger, so as to reach and bring to the surface the deepseated springs.

In the metropolis, every one knows the great outcry which has of late been made about the polluted state of the Thames water for domestic purposes, arising from this river being the receptacle of the drainage waters of that overgrown city. In point of fact, (as noticed by our distinguished countryman, Mr. Stevenson, engineer,) the waters of the Thames are changed or renewed very slowly, nearly. the same body of water moving upwards and downwards as the tide flows or ebbs. The inhabitants of London, therefore, may actually be said to be receiving into the stomach what had formerly passed through the public drains. This has become a subject of so much notoriety and interest, that government has of late made it a matter of public inquiry, and has procured the report of a committee of professional men, consisting of a physician, a chemist, and a civil engineer. The effect of these movements has been to produce numerous plans for supplying the city from a purer source, and also for filtering the water which it already possesses. Among these may be mentioned a plan by Mr. James White, engineer, of Oxford street, London, and another by Messrs. Stirling and Son, of Lambeth, who have invented a machine called the "Rapid Filter," and obtained a patent for it. Having no drawing of Messrs. Stirling's apparatus,

we shall at present confine ourselves to a notice of Mr. White's "Patent Artificial Spring," as given by himself.

"When new inventions, which promise to be of public utility, present themselves to our notice in a simple form, a degree of surprise is excited, that they should hitherto have eluded the research of ingenious men, whose lives have been devoted to mechanical pursuits. It is certain there are but few things of greater importance to the comfort of every family than water, which shall be good in quality, and provided in sufficient quantity for all the purposes of domestic use. That both these effects are produced by this invention, will be best shown by a description of the annexed diagram, and an account of the experiment, as tried at the house of the nobleman who was the first to patronize the design. The figure, as

shown in the diagram, is a section through the centre of the machine, which shows the whole of its interior construction. The cistern containing the water is not introduced, as its height would exceed the limits of the diagram; but let the small pipe, P, be supposed to communicate with it, and be of any length, from 10 to 100 feet: it is, however, necessary to bear in mind, that the quantity filtered will

always be proportioned to the area of the stone multiplied into the height of the column or pipe. The advantage, therefore, of employing a high cistern to supply the machine, requires no other recommendation.

"Three years ago, in the south of Russia, in the government of Poltava, when, on a mission appointed by the late emperor to examine the mechanical and agricultural state of that part of the Russian empire, it fell to my lot to give a design for filtration on a large scale. To effect that object, I introduced the water to be filtered below a bed of sand and gravel: it was intended for the purpose of washing wool, consequently did not require that purity produced by this invention. But at the house of the nobleman I have already alluded to, I attached a half inch leaden pipe to a cistern, which was already fixed thirty-five feet above the ground-floor, where I placed the machine. The other end of the pipe I made water-tight, by fixing it to a nozzle in the apparatus, below a proper filtering stone. Upon turning the cock, A, which shuts off the communication betwixt the machine and the cistern, the water rushed down from the cistern with great force, and very soon displaced all the air contained in the apparatus through the pores of the stone S; after which, the water began to ascend, and to flow in a filtered stream at the cock, B, so as to fill a gallon measure in about two minutes' time. Its appearance in small bubbles, rising through every pore in the stone, from the great pressure of the column of water contained in the small pipe, P, suggested to me the name which I have given it, of an artificial spring; and further experience has fully convinced me, that I have not applied to my invention an unmerited title. From the construction of the apparatus, the sediment and animalculæ will fall to the bottom, and be drawn off at the under cock, C, and run off by the waste pipe, E. In cases where several gallons are wanted at the same time, and it might be inconvenient to wait until it be filtered, shut the cock, B, leave A open, and in a few minutes, with a pressure from a cistern of thirty feet high, eight or ten gallons will be found filtered in the top part of the apparatus, which can be drawn off at B for immediate use, as required. Should it filter more than the top reservoir contains, while A remains open, it will run off waste at F; the cock, A, can be so constructed as to shut of its own accord, but in this case the machine would not be so simple. The cock, A, is of a peculiar construction, and well merits the attention of the reader: at the same time that it shuts off the communication betwixt the machine and the cistern, it opens, when turned one way, through the tube D, a small passage to the atmosphere. By this. contrivance, the filtered water in the top part of the machine is allowed to subside the contrary way through the stone, a process which must naturally tend to wash its pores clean; and we know that all filtering substances are subject to get clogged up, from particles of fine sediment lodging in their pores. But what back filtration does not remove in my invention, another beautiful and simple phenomenon completely effects. Open the under cock, C, and then shut it again as fast as possible: this will produce an immense pressure on