ELECTRO-MAGNETIC ENGINE.
(To the Editor.)

SIR.-I send you an account of a very convenient electro-magnetic engine, which I have constructed for my own use: it does not differ in principle from that of Mr. Bachhoffner, which you described in your first volume, nor yet from others since inserted in your valuable Magazine, but it is more convenient than they are, on account of the facility of attaching the usual electro-magnetic apparatus to it, especially by the introduction of the universal discharger.-It is as follows:

ZA, are two brass pillars, with holes drilled on top of each for the brass wire B. C, a cam or break with pulley on back of an upright pillar Z, with mercury in hole at top to break connection; to use the table, take out the wire B, then put two wires and joints, like D, into the holes of A and Z, with the table between them. This table you may show many experiments on. The machine altogether answers very well; it requires a large coil of primary wire to make the iron bar a strong magnet to cause the buckets to rotate; one end of the primary coil goes to the pillar with mercury on the top end of it at Z, the other end goes to the binding screw E. There is a wire soldered to pillar A and goes to binding screw F; one end of the secondary coil goes to binding screw G, the other end goes to binding screw H. Put a little powder on the top of pillar Z, turn the multiplying wheel, and it will fire the powder instantly; likewise on the table, if the two wires be put in the place of the brass wire B. The pillar Z has a small cannon screwed in near the top, with touch-hole at the end, about of an inch above the mercury; to fire the cannon, put a little gunpowder on the top of the mercury, then turn the multiplying wheel, and the cannon goes off. The brass wire B must work clear in the hole on top of the pillar Z, not to touch the pillar any where only on the top of the mercury. If you think the above worth your notice, the insertion will oblige, yours, Mile Gate, Ripon.

MICROSCOPIC

W. SKIPSEY.

OBJECTS.

We have repeatedly been referred to for a list of microscopic objects, such as will at once show the powers of an instrument, yield instruction and amusement, and yet such, that amateurs in the country may procure and mount them for their own use. We have somewhat neglected this subject lately, because we often adverted to it in the first volume, but the description of a microscope in our last part has again drawn upon us several inquiries; we shall best answer them, by referring our readers to an excellent little work, entitled "A List of Two Thousand Microscopic Objects," by Mr. Pritchard, the well-known author of several works on infusorial animals, and a celebrated maker of microscopes in Fleet Street. We have carefully looked over the list, (which is published at a shilling only,) and are obliged to testify to the choice selection of objects, as well as the other interesting matter which it contains on mounting, collecting, &c. To show the nature of the introductory remarks, we take the following almost at random :

"The eggs of birds are oval, but those of insects assume a vast variety of forms: some are furnished with covers : the surfaces of many are elegantly embossed or fluted, whilst others, as those of the Bug (Cimex lectularius,) have their surface curiously granulated. Those given in the list will be found among the most interesting for microscopic

observation. They require in most cases to be viewed by reflected light, and with moderate amplification; namely, between 20 and 60.

"Human Hair.-In the adult, the friction of the hairs against each other is such, that their exterior structure is seen with difficulty. From a consideration of this circumstance, and finding the hairs of infants frequently matted, or felted together in small knots, after washing, arising from its jagged surface, I was induced to examine the latter, and finding the asperities much more decided than in that from the adult, I procured some specimens from a babe only two hours old, in which the imbricated structure was very distinct. On mounting, however, a specimen of this hair in Canada balsam, the exterior characters were obliterated.

"Hair of Caterpillars.-The hairs of some species, when examined by the microscope, resemble branches of the black thorn; and others are formed with branches on each side, like a fan, resembling the feathers of the peacock's tail.

"Butterflies, moths, and many other insects, are covered with scales or feathers, overlapping each other like the tiles of a house. They vary greatly in form and size, and from the difficulty with which the structure of many of them is developed by the microscope, they become excellent tests of its penetrating power. In the list, I have introduced the most interesting and peculiar, and it may be observed that such are seldom found on the red parts of the wing; the white or blue yield the greatest variety.

"If the crystalline lens in the eye of a fish be minutely examined by the aid of the microscope, it will be found to be composed of a number of concentric strata or layers, somewhat resembling the coats of an onion. One of these laminæ, separated, and placed under a powerful microscope, will be seen to consist of flat fibres or bands, arising from each pole of the globular lens, and expanding towards the equator, like the spaces between the meridians on the artificial globe. The edges of these fibres are serrated, and fit into each other like the teeth of a double rack, or the sutures of the human skull. Sir David Brewster, who first minutely examined the structure of these lenses, has accurately measured the width of the bands. (See Phil. Trans. 1833.) He found a single lens, fourtenths of an inch in diameter, from the eye of a cod, contained five millions of these flat fibres, and 62,500 millions of serratures or teeth. Whether as opaque or as transparent objects, I have been much delighted with them. Viewed as the former, an amplification of 250 times is sufficient, but as the latter, 400 times linear may be employed with advantage.

"The method of mounting in alcohol or spirit of wine is as follows:-Take a slip of glass, and cover it on one side with a coat of painters' whitelead, leaving a space in the middle large enough to contain the object to be mounted ;-when this coat is dry, add another, and proceed thus until a sufficient thickness is obtained for the inclosure of the object to be mounted. The next thing is to procure a clear piece of mica, free from veins and flaws, and rather smaller than the slip of glass. Fill the cavity above referred to with spirit of wine, place the object therein, and cover it with a plate of mica, which must be brought into close contact with the whitelead, by gently pressing it with a smooth piece of wood from one extremity to the other, so as perfectly to expel the air-bubbles. In a few days the whitelead will have become hard, and if the mica be sound,

the inclosed specimen may be preserved for years. In plants it must be remembered that excepting their elementary tissues, much of their delicacy is destroyed by this method of mounting, although in many cases it is still highly desirable.

"The most interesting active phenomenon exhibited by the microscope is the circulation of the nutritious fluids in animals and plants. In the former, the globules of blood may be seen passing rapidly along the capillary ends of the arteries into those of the veins, when the intervening membrane is sufficiently diaphanous, as in the ear of the young mouse; the fins and tail of the carp, gold-fish, stickleback, tadpole, and of most small fish; and in the web between the toes of the frog, lizard, eft, &c. For these purposes, a magnifying power from 100 to 250 times linear is sufficient.

In the

"In the Arachnoida (Spider tribe,) at the joints of the legs, I have observed the circulation very distinct, the current of dark globules passing rapidly at each pulsation of the dorsal vessel. antennæ and wings of terrestrial insects, it has also been seen when they have just emerged from the chrysalis, as in the Perla viridis and Semblis bilineata. In several aquatic larvæ and small crustacea, the circulating fluid traverses the limbs, antennæ, and tail, and thence moves along the dorsal vessel towards the head, and down the sides of the body, in cavities, and not distinct vessels; hence called diffused circulation. The most favorable subjects for viewing this are the following:-Larva of the ephemera. (The recent discovery of the beautiful mechanism of the dorsal vessel of this larva by Mr. Bowerbank is fully confirmed by the careful dissections of Mr. Newport, who, with much perseverance, has extended these inquiries to the other states of insects.) Larva of hydrophilus; small dytiscus; agrion puella. (In this elegant larva I have not observed the circulation in the legs to extend beyond the haunches.) Libellula; round lynceus; fresh-water shrimp ; water hog (Oniscus); Ligia; water flea (daphnia pulex); &c. Power 100 to 300 times.

"In several of the polypiferous zoophytes, as the tubularia indivisa, sertulariæ, campanulariæ, plumularis, &c. Mr. Lister has, by means of the achromatic engiscope, discovered a circulation to exist, which in many respects resembles that in plants. See Phil. Trans.

"The circulation in plants termed cyclosis is a revolution of the fluid contained in each cellule, and is distinct from those surrounding it. It can be observed in all plants in which the circulating fluid contains particles of a different refractive power or intensity, and the cellules of sufficient size and transparency. Hence all lactescent plants, or those having a milky juice, with the other conditions, exhibit this phenomenon. The following aquatic plants are generally transparent enough to show the circulation in every part of them :--Nitella hyalina; nitella translucens; chara vulgaris; and caulinia frigalis. In the frog-bit (hydrocharis) it is best seen in the stipulæ of the leaves and the ends of the roots. The magnifying power suited for the above are between 100 and 250 times linear. In the spider-wort (tradescantia virginica) it is seen in the filaments surrounding the stamens of the flower: power 300 to 500 times linear. In the common groundsel (senecio vulgaris) it is said to be seen in the hairs surrounding the stalks and flowers. In the valisneria spiralis circulation may be seen in sections of the leaf."

ETCHING AND DYEING FIGURES ON

IVORY.

BY J. CATHERY.

THE usual mode of ornamenting ivory in black is to engrave the pattern or design, and then to fill up the cavities thus produced with hard black varnish. The demand for engraved ivory in ornamental inlaying, and for other purposes, is considerable, although the price paid for it is not such as to encourage artists of much ability to devote themselves to this work, which consequently is trivial in design and coarse in execution. Mr. Cathery's improvement consists in covering the ivory with engraver's varnish, and drawing the design with an etching needle; he then pours on a menstruum composed of one hundred and twenty grains of fine silver, dissolved in one ounce measure of nitric acid, and then diluted with one quart of pure distilled water. After half an hour, more or less, according to the required depth of tint, the liquor is to be poured off, and the surface is to be washed with distilled water, and dried with blotting paper; it is then to be exposed to the light for an hour, after which the varnish may be removed by means of oil of turpentine. The design will now appear permanently impressed on the ivory, and of a black or blackish brown color, which will come to its full tint after exposure for a day or two to the light.

The property which nitrate of silver possesses, of giving a permanent dark stain to ivory and many other substances has been long known; but Mr. Cathery has the merit of having advantageously applied it in a department of art in which it is likely to be of considerable service, by improving the quality of the ornament, and at the same time of diminishing the cost. Varieties of color may also be given by substituting the salts of gold, platina, copper, &c. for the solution of silver.

EARTHQUAKES.

ANarthquake consists of a violent agitation of the

accompanied by various other phenomena more or less singular and destructive in their effects, but by no means uniform in character, as the following enumeration of concomitant circumstances, gleaned from the accounts of various earthquakes that have occurred in ancient and modern times, will sufficiently evince. Earthquakes are usually preceded by a general stillness in the air, and an unnatural agitation of the waters of the ocean and of lakes. The shock comes on with a deep rumbling noise, like that of a carriage over a rough pavement, or with a tremendous explosion resembling a discharge of artillery, or the bursting of a thunder cloud; and sometimes heaves the ground perpendicularly upwards, and sometimes rolls it from side to side. The single shocks of an earthquake seldom last longer than a minute, but they frequently follow one another at short intervals for a considerable length of time. During these shocks large chasms are made in the ground, from which sometimes smoke and flames, but more frequently stones and torrents of water, are discharged. In violent earthquakes, these chasms are sometimes so extensive as to overwhelm whole cities at once. In consequence of these shocks, also, whole islands are frequently sunk and new ones raised; the course of rivers is changed seas overflow the land, forming gulfs, bays, and straits; sometimes disrupting the land into islands, and sometimes joining them to the continent.

There is no portion of the earth's surface, whether it be land or water, that is not more or less subject to earthquakes; and records of their destructive effects have been transmitted to us through every age. The first earthquake particularly worthy of notice was that which, in A.D. 63, destroyed Herculaneum and Pompeii. In the fourth and fifth centuries, some of the most civilized parts of the world were almost desolated by these awful visitations. Thrace, Syria, and Asia Minor, according to contemporary historians, suffered most severely. On the 26th of January, A.D. 447, subterranean thunders were heard from the Black to the Red Sea, and the earth was convulsed, without intermission, for the space of six months; and in Phrygia, many cities and large tracts of ground were swallowed up. On the 30th of May, A.D. 205, the city of Antioch was overwhelmed by a dreadful earthquake, and 250,000 of its inhabitants are said to have been crushed in its ruins.

In the year 1346, Asia Minor and Egypt were violently shaken; and in the following year severe earthquakes were experienced in Cyprus, Greece, and Italy.

In 1692, the island of Jamaica was visited by a terrible earthquake, in which enormous masses of earth were detached from the Blue Mountains; and vast quantities of timber, hurled from their flanks, covered the adjacent sea, like floating islands. It was during this earthquake that the city of Port Royal, with a large tract of adjacent land, sunk instantaneously into the sea. In the following year great earthquakes occurred in Sicily, which destroyed Catania and 140 other towns and villages, with 100,000 of their inhabitants.

Since the records of history, there have been no earthquakes equal in intensity to those which ravaged different parts of the world in the eighteenth cen. tury. Passing over the convulsion which in 1746 nearly laid waste Lower Peru, and those by which in 1750 the ancient town of Concepcion in Chili was totally destroyed, we come to 1755, when the city of Lisbon was almost wholly destroyed by one of the most destructive earthquakes which ever occurred in Europe. It continued only six minutes; but such was the violence of the convulsion, that in that short space upwards of 60,000 persons are said to have perished. The phenomena that accompanied it were no less striking. The sea first retired and laid the bar dry; it then rolled in, rising fifty feet or more above its ordinary level. The largest mountains in Portugal were impetuously shaken from their very foundations; and some of them opened at their summits, which were split and rent in a wonderful manner, huge masses of them being thrown down into the subjacent valleys. But the most remarkable circumstance which occurred at Lisbon during this catastrophe was the entire subsidence of the new quay, called Cays de Prada, to which an immense concourse of people had fled for safety from the falling ruins. From this hideous abyss, into which the quay sunk, not one of the dead bodies ever floated to the surface; and on the spot there is now water to the depth of 100 fathoms. This earthquake excited great attention from the incredibly great extent at which contemporary shocks were experienced. The violence of the shocks, which were accompanied by a terrific subterranean noise, like the loudest thunder, was chiefly felt in Portugal, Spain, and northern Africa; but the effects of the earthquake were perceived in almost all the countries of continental Europe, and were

even experienced in the West Indies, and on the Lake Ontario in North America. Ships at sea were affected by the shocks as if they had struck on rocks; and even at some of the Scottish lakes, Loch Lomond in particular, the water, without the least apparent cause, rose to the perpendicular height of two feet four inches against its banks, and then subsided below its usual level. During the next twenty years, various earthquakes occurred in dif ferent parts of the world, attended with more or less destructive consequences. In 1759, Syria was agitated by violent earthquakes, the shocks of which were protracted for three months, throughout a space of 10,000 square leagues, and levelled to the ground Accon, Saphat, Balbeck, Damascus, Sidon, Tripoli, and many other places. In each of these places many thousands of the inhabitants perished; and in the valley of Balbeck alone, 20,000 men are said to have been victims to the convulsion. In 1766, the island of Trinidad and great part of Columbia were violently agitated by earthquakes. In 1772, the lofty volcano of Papandayang, the highest mountain in Java, disappeared, and a circumjacent area, fifteen miles by six, was swallowed up. In 1783, the north-eastern part of Sicily and the southern portion of Calabria were convulsed by violent and oft-repeated shocks, which overthrew the town of Messina, and killed many thousands of its inhabitants, as well as many persons in Calabria. In the same year the islands of Japan, Java in 1786, Sicily and the Caraccas in 1790, Quebec in 1791, and the Antilles and Peru in 1797, were violently agitated by convulsions of this kind.

Since the commencement of the present century, various earthquakes have occurred both in the Old and New World. In 1811, violent earthquakes shook the valley of the Mississippi, by which lakes of considerable extent disappeared, and new ones were formed. In 1812, Caraccas was destroyed, and upwards of 12,000 of its inhabitants buried in the ruins. In 1815 the town of Tombora, in the island of Sumbawa, was completely destroyed by an earthquake, which extended throughout an area 100 miles in diameter, and destroyed 12,000 persons. In 1819, a violent earthquake occurred at Cutch, in the Delta of the Indus, by which, among other disastrous consequences, the principal town, Bhoog, was converted into a heap of ruins. In 1822, Aleppo was destroyed by an earthquake. ln the same year Chili was visited by a most destructive earthquake, from which the coast for 100 miles is stated to have sustained an elevation of from two to four feet, while about a mile inland from Valparaiso, it was raised from six to seven feet. In 1827, Popayan and Bogota suffered severely from earthquakes, during which vast fissures opened in the elevated plains around the latter city. In 1835, the town of Concepcion, in Chili, was entirely demolished by an earthquake. In 1837, the countries along the eastern extremity of the Mediterranean, especially Syria, were violently agitated by an earthquake, which caused great damage to the towns of Damascus, Acre, Tyre, and Sidon, and entirely destroyed Tiberias and Safet. Such are some of the most violent earthquakes that have occurred within the period of authentic history. The reader will find in Poggendorf's Annalen lists of the different earthquakes that have taken place within the last twenty years; and from these it will be observed that scarcely a month elapses without being signalized by one or many convulsions in some part of the globe. Shocks of earthquakes have at different