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excellent works of other distinguished authors, to Mr. Jabez Hogg belongs the credit of having done the most for the popularization of microscopical science. In the preface to the present and sixth edition of his work, he justly observes that “a sale of fifty thousand is an unprecedented event for a work of this kind.” Since the publication of his fifth edition, much light has been thrown upon various subjects then imperfectly understood, and some changes have taken place in power and apparatus. It was, therefore, necessary that a considerable portion of the matter in that edition should be modified or rewritten, and that entirely new subjects, such as the application of the spectroscope to the microscope, should be described. The present (sixth edition) will be found to contain a good deal more matter than the last, and it is enriched by eight beautifully coloured plates, which will add greatly to its popularity and value. It makes indeed so handsome and attractive a volume that it may well take its place amongst the gift-books of the season, and if accompanied by one of the numerous forms of microscope which it describes, it will supply intelligent families with a fund of instructive enjoyment. The average and deplorable ignorance of the upper and middle classes in this country on scientific matters, and the tendency to resort to frivolous amusements by way of killing time, is a painful fact against which our social reformers must struggle manfully, and although we do not wish to imitate the professors in the Bourgeois Gentilhomme in exaggerating the value of any particular pursuit, we feel amply justified in recommending the microscope as one of the most effective instruments for general instruction. To purchase a microscope with a few slides, and then to make unsuccessful efforts at the examining of common objects, is a process which has been tried hundreds of times with inevitable disappointment. To enjoy or appreciate the performance of a microscope, a considerable amount of scientific knowledge must be obtained. To manage the instrument well is impossible without some knowledge of optics : objects cannot be prepared, so as to be seen properly, without an acquaintance with their structure, and the acquisition of manipulative power. Vegetables and animals, either whole or in part, will afford little amusement without some acquaintance with, at least, the elements of physiology, natural history, botany, chemistry, etc. Thus the employment of the microscope may be made a constant stimulant to various studies, and any knowledge gained immediately repays the student by giving greater interest to old objects, or suggesting important points to be ascertained with regard to new ones. The task which Mr. Hogg has proposed to himself, and carried out with well-known skill, is to smooth over the difficulties which beset beginners, and he has achieved a high degree of success in the difficult art of combining the popular with the scientific. Many writers who undertake to be popular only twaddle about science, and their productions should be avoided as likely to mislead. Mr. Hogg adopts a strictly scientific method, but by avoiding the needless use of hard words, and by a good logical arrangement, he brings complicated subjects within the reach of ordinary intelligence and reasonable attention. The first chapter of his work in its present state relates to the history of the invention and improvements of the microscope, and we may notice parenthetically that the publisher has unwisely placed the words “ History of the Microscope" as the external title shown on the binding, thus misleading those who see no more as to the character of the book. The second and third chapters describe at length various instruments and apparatus, modes of preparing objects, etc.

The second part of the volume consists of six chapters, the first devoted to the vegetable kingdom, the second to the protozoa, and other forms up to the echinodermata, the third begins with the polyzoa, and ends with the annelida, the fourth relates to insects and spiders, the fifth deals with the microscopic structure of the vertebrata, and the sixth refers to crystals, polarization, spectrum analysis, etc., etc.

Although we recommend this work to intelligent beginners, it must not be supposed that it will not prove of service to more advanced students. It is indeed adapted to both--to the former from its simplicity and clearness, and to the latter from the care taken to bring each subject down to date. Thus the physiologist will find Mr. Whitney's elaborate and interesting researches into the respiratory apparatus of the tadpole fully explained and illustrated by a fine series of coloured drawings.

We feel bound to pronounce Mr. Hogg's sixth edition an honour to English microscopy, and we have no doubt we shall soon congratulate him on the appearance of a seventh, in which we recommend him to reconsider his reprint of the statement so commonly made about the highly composite character of the spider's thread. We pointed out last year that by placing an earwig in the web of the handsome garden spider, Epeira diadema, the use of the multiplicity of spinnets may be easily observed. The spider shoots out a sheaf of her silken threads, the ends of which stick to the earwig, which she then pats round and round, as if she were roasting him on a spit, until he is swathed like a mummy in the silken winding-sheet which the numerous spinnets enable her to form in a few seconds.

We must, however, while amply recognizing the merits of Mr. Hogg's book, protest against the injustice done to one of our great firms-Messrs. R. and J. Beck—whose numerous excellent forms of microscope are most unaccountably and unfairly omitted.

INTRODUCTORY TEXT-BOOK OF GEOLOGY. By David Page, LL.D., F.R.S.E., F.G.S. Seventh and Enlarged Edition. (Blackwood and Sons.) ADVANCED TEXT-BOOK OF GEOLOGY, DESCRIPTIVE AND INDUSTRIAL. By David Page, F.R.S.E., F.G.S., etc. Fourth Edition, revised and enlarged. (Blackwood and Sons.) – The second edition of Mr. Page's excellent " Introductory Text-Book" was published in 1855; the third in 1857; the fourth in 1860; the fifth in 1861; and the sixth in 1864, and now come the seventh in 1867. These simple facts testify to the great merit of the work as a simple

intelligible introduction to a comprehensive and difficult science. We need only repeat the favourable opinion we have before expressed of Mr. Page's labours, and add that his volume is well illustrated, and so low in price as to be within the reach of students of very small means-a fact which we consider important. Mr. Page's larger work made its first appearance in 1856, and the demand for a fourth edition, so soon as 1867, shows the welldeserved repute in which it is held. The present edition appears to notice all recent facts of importance. It is well printed and well illustrated.

PROGRESS OF INVENTION.

A New HYDRAULIC CEMENT.—Many excellent hydraulic cements are already known. A very simple and effective one has recently been added to the number by M. Lorel. It is merely a basic hydrated oxy-chloride of magnesium, and it is formed by adding a more or less concentrated solution of chloride of magnesium to magnesia. The magnesia may be very conveniently obtained by adding quick-lime to the mother liquor, that is the residue in salt works, which contains chiefly chloride of magnesium; magnesia will precipitate, and is to be calcined. Double chloride of calcium, and magnesium will remain in the liquid; and if chalk or lime are added, an excellent material for hardening common plaster on walls, etc., will be obtained; or the liqnid itself may be used for moistening the materials in making the cement. Magnesiam cement is extremely plastic, and forms a substance like arble. It takes colour well, and it has such agglutinative power, that one part of it is capable of uniting twenty parts sand. It is, therefore, expected to constitute a means of rendering building easy, where building materials do not exist.

NEW TUBULATED Syphon.—The common syphon, though made of glass, cannot it is obvious, be used with corrosive fluids without great inconvenience. A partial remedy, which consists of an accessory

tube containing a bulb, has been long employed. The air is drawn by means of this tube from the lower end of the longer leg of the syphon: the necessary vacuum being thus made, the liquid ascends, and soon begins to flow. The bulb in the accessory tube with moderate care, almost prevents the danger of any of the liquid being drawn into the mouth. M. Zaliwski-Mikorski has, however, invented a syphon which is perfectly safe, and very simple; and in which blowing is substituted for suction. In his instrument, the accessory tube is attached to the lower extremity of the shorter leg of the syphon, and, on blowing into it, the liquid will be drawn up, and the syphon filled, provided the place of attachment is not too far from the liquid.

PRINTING ON GLASS.-Very cheap and beautiful products are now obtained by printing on glass; a large amount of the fine effect of stained glass being had for a very small portion of its cost. The inventor, M. De Mothay, uses for colouring matter pigments mixed with a solution of silicate, or silico-borate of potash and lead, and a solution of resin in turpentine. The printing is effected with rollers, and the colours are vitrified by heat, no distortion taking place.

A New ANEMOMETER.- This self-registering instrument, the invention of M. Radan, consists of a pencil moving uniformly down a vertical cylinder, or from the centre to the circumference of a disc, on each of which paper has been placed. If the cylinder, or disc, is stationary, the line drawn on the paper placed on the cylinder will be perpendicular to the circumference of its base; and that on the paper placed on the disc will correspond with one of the radii of the disc. The pencil is connected with a Robinson anemometer in such a way that, when the cups have made a certain number of revolutions, it is lifted from the paper, an interruption being thus produced in the line drawn upon it. And the cylinder, or disc is made moveable on an asis, at the upper end of which is fixed an ordinary weathercock. The paper on the cylinder, or disc, is divided by lines into spaces which correspond with equal portions of time. The interruption, therefore, in the line made by the pencil, corresponding to a given time, will show the velocity of the wind during that time. And the deviations of the pencil-line from a round line will show its direction during any given time.

A New CANNON.-It is a matter of great importance that the force produced by the explosion shall be gradually communicated to the projectile. The inertia of the latter renders this necessary; since, though motion may be communicated very rapidly, it still requires a certain time for transmission. A powder may explode with such velocity, as that instead of the projectile being driven forward, the gun shall be burst; such would be the case were any fulminating compound substituted for gunpowder. Among the means used for securing a gradual communication of the explosive force to the ball is a cannon recently invented in America, and which is said to afford excellent results. Instead of the powder being accumulated in one chamber behind the ball, only a portion of it is placed there, the remainder being introduced into lateral chambers in front of the ball, and communicating by openings with the interior of the gun; when the powder has been placed in any one of these chambers, the opening which forms the communication between it and the exterior is closed by a screw. As soon as all have been charged, the piece is ready to be fired; and the instant the ball has passed the opening leading to one of these chambers the intensely heated gases following the ball, enter it, and exploding the powder which it contains, a new impulse is given to the projectile. This takes place after the latter passes each of the chambers ; the explosive force of the powder being separated into successive portions and therefore rendered more effective. The explosion being divided there is less danger of the gun bursting; but the complication, and the time required for loading will be found more or less objectionable.

A SELF-REGISTERING MARINER'S COMPASS.- A mariner's compass which is capable of registering the ship's course, and is by no means complicated, has been invented by the Baron Webel-Jarlsberg, a Nor. wegian nobleman, connected with the marine. A time-piece, is placed

in the upper part of the binnacle, and is so constructed, that every two minutes it lets fall a very small leaden shot. This shot, falling on the moveable card of the compass, is conveyed by a channel to an aperture in the card, in which is fixed a small glass tube, and passing through this tube, it falls into some one of thirty-two radial compartments, into which a small box, which has been placed under the compass, is divided. As the box is immoveable, and the card is moveable, it depends on the course the ship is following, which compartment a given shot shall fall into; and the number of shots found in a given compartment, will show the length of time during which the vessel was steered in the direction corresponding to that division, since each shot answers to a space of two minutes. The contrivance is very ingenious, but, as at present arranged, it has certain defects : it does not tell exactly the length of time during which the vessel was steered in any direction: and at the end of a given period, only the sum of the times during which a given course was held, and not those times themselves can be ascertained. This, however, is not so inconvenient as might at first be supposed.

SIMPLIFICATION OF THE GALVANIC BATTERY.—It has been found by M. Manuelli Giacomo, that sulphatə of zinc may be substituted for the sulphate of copper in a Daniel's battery, without lessening the power of the battery. The effects of such a substitution is a considerable saving of expense, since the cost is merely that of the zinc consumed. He found also that a very good galvanic current will be produced, if zinc is substituted for the copper of the battery. In this case, the zinc constitutes both the electro positive and electro negative metal.

New APPLICATION OF GELATINE.—The addition of glycerine to gelatine imparts to it new and valuable properties: the mixture solidifies on cooling, without ceasing to be ductile. Common glue mixed with one-fourth glycerine, becomes very similar in properties to caoutchouc, thus it will remove pencil marks from paper :

it

may, also be used as a varnish.

A New PHOTOMETER.—The transparency of the air on the approach of rains, so that distant mountains become more distinctly visible, has long been recognized as an almost certain prognostic of approaching rain. This transparency is usually considered to arise from the presence of watery vapour; but is said to be partially due to the rendering transparent, or precipitation of, organic matter. This is inferred from the fact that the air coming across arid deserts is transparent in dry weather, but the contrary in moist weather, when it has traversed tracts in which the heat rapidly and abundantly developes animal and vegetable life. In a moist atmosphere, the distant mountain is seen more clearly, because the watery vapour contained in the air either renders the germs of vegetables, etc., transparent, or makes them so heavy that they fall to the ground. And as the sanitary condition of the atmosphere is intimately connected with the

presence of organic matters in it, an instrument capable of measuring the transparency of the air, and, therefore, of indirectly indicating the amount of organic matters which it contains, becomes of some importance. M. De La Rive has recently constructed an

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