THREE-WHEELED ORRERY.

To the Editor.

SIR. I inclose for insertion in your Magazine, a perspective view of the external arrangement of a three-wheeled orrery, which I invented during my residence in London, early in the year 1837.

The wheel-work, &c., is inclosed within a large circular frame of mahogany, of about eighteen inches in diameter, E E, on the upper surface of which is carefully laid down the signs of the ecliptic-the days of the month, and hours of the day, as delineated. The sun is represented by a ball, S, in the centre, gilded, and is six inches in diameter, to the right of which is a small terrestial globe, F, three inches in diameter, on which are engraven the several countries of the world, with circles of latitude and longitude, and is surrounded with a small engraven ecliptic circle, K, and circle of altitude, L. The ball, E, representing the earth, is inclined at an angle of about 234°, and is attached to an axle which ascends from the wheel-work, and by virtue of which connexion it preserves its parallelism in its circular journey round the sun, thereby familiarly exhibiting the cause of the change of the seasons, and different lengths of day and night throughout the year, &c. Immediately under the earth is fixed a small circular dial-plate, on which is engraven the twenty-four hours of day and night, which is very serviceable in attaining the time of terrestial phenomena. Under this dial-plate is another, which is stationary, and on which are engraven the days of the moon's age; and lastly, another circle is attached to the wheel-work, and on which is laid down the degrees, &c. of the nodes of the moon's orbit. This ring or circle is inclined at an angle of about 54° to the plane of the frame, E E. This ring has a retrograde motion in the ecliptic in the space of 18 years and 224 days, which is nearly the period of the nodes. Between the circles of the hour, at the foot of the earth's axis, and the circle of the moon's age, a horizontal arm extends from the wheel-work, and carries a perpendicular arm, H, which is partly hollow, for the purpose of affording a vertical motion suitable to the moon's declination, &c. M is a small ball of about three-quarters of an inch in diameter, and is furnished with a black cap, which exactly covers from view one-half of the lunar globe, and to which is attached a kind of forked arm extending upwards, and has a connexion with the sun through the medium of the slight horizontal bar, W, and joined to the sun at 1. In short, with this very simple orrery, the following very interesting astronomical phenomena may be distinctly ascertained, and which, so far as I know, is the first time such important results from such simple causes have been effected :

Phenomena exhibited by the New Orrery. 1. The unequal lengths of day and night during the year, and hence the cause of the vicissitude of the seasons.

2. The sun's place in the ecliptic, declination, &c. 3. The periodic and synodic revolution of the moon. 4. The moon's diurnal rotation on its axis. 5.-The age and phases of the moon. 6. The motion of the moon's orbit. 7.-The motion of the apogee of moon's orbit. 8.-The eclipses of the sun, moon, &c.

All the above being effected by a very peculiar arrangement of only three wheels and a pinion. I may add that the moon goes round the earth in the ma

chine in 29 days, 12 hours, 44 minutes, 25 seconds, and round its own axis in the same time. The earth is moved by hand, is assumed to perform its journey round the sun in 365 days, 5 hours, 48 minutes, and 9 seconds. The moon's orbit makes a retrograde movement through all the signs and degrees of the great ecliptic circle in 6,798 days, 8 hours, and that of the apogee in 3,231 days, 18 hours, tropical time.

I generally exhibit this simple orrery in my astronomical lectures, and as it gives general satisfaction, and as a number wish to have copies of its form, I send it to you, in order that they may see it engraved in your widely-circulated Magazine, of which I have been a subscriber since its commencement. I may, at some future period, render you a description of the wheel-work of this instrument, as also of a variety of original and various astronomical machinery, should the present be acceptable to your readers.

E. HENDERSON.

IMPROVEMENT OF THE DAGUERREO. TYPE.

THE process of Mr. Wolcroft, an American, patented in England by Mr. Beard, for quickening the action of the Daguerreotype, so as to produce the effect in a few seconds, is now carried into practice at the Polytechnic Institution in taking likenesses. The room fitted up for the purpose is at the top of the building in Cavendish-square. The roof is composed for the most part of large sheets of plate-glass, stained blue to soften the light, and this glass roofing traverses so as to meet the rays of the sun at any part of the day. The sitter is placed on an elevated platform, with a support for the head, and the camera obscura rests on a shelf a few feet distance from him. The construction of the camera itself, as thus applied, consti tutes part of Mr. Woleroft's patent. Instead of using a lens to refract the rays of light to a focus, he employs a reflector, about seven inches diameter. By this means a much greater number of the rays issuing from the object are concentrated within a given space than could be otherwise accomplished, and the image is consequently the brighter. The speculum may also be placed nearer to catch the rays of light than a lens, and this also affords an additional increase of collected rays in the image. The silvered plate, prepared with a coating of the vapors produced by iodine mixed with nitric acid, or with bromine, so as to quicken the action of the light, is put into the focus of the reflecting mirror. The person whose likeness is to be taken keeps his face steady for a few seconds, and the effect on the iodine coating is produced. The plate is then taken away, and excluded carefully from the light until it has been exposed to the vapor of mercury, which attaches to the parts acted on by the light, and the image becomes visible-a perfect fac-simile of nature. Before the plate is exposed to the light, the iodine is washed off, and all further change is thus prevented by exposure. The time occupied by the process varies with the intensity of the light. Some likenesses were taken in five seconds, others occupied twenty, according as the sky was clear or clouded. The difficulty experienced, is to determine the exact time that the plate should remain exposed to the vapor of mercury, the requisite time is at present determined only by trial, and the judg. ment of the operator. It must therefore require some practice to produce the best possible effects.

DISTRIBUTION OF ANIMALS.

On a superficial view, vegetables seem more abundant than animals; so contrary, however, is this to fact, that the species of animals, when compared with those of plants, may be considered in the proportion of 10 to 1. Hence it follows that botany when compared with zoology, is a very limited study: plants, when considered in relation to insects alone, bear no proportion in the number of the species. The phanerogamous plants of Britain have been estimated in round numbers at 1500, while the insects that have already been discovered in this country (and probably many hundreds still remain unknown) amount to 10,000, which is more than six insects to one plant. It is therefore obvious that the knowledge acquired of the geographical distribution of animals, in comparison with what is known of plants, is slight and unsatisfactory: it is likewise attended with difficulties inseparable from the nature of beings so numerous and diversified, and which will always render it comparatively imperfect. It rarely happens that a single specimen of a plant is found isolated; the botanist can therefore immediately arrive at certain conclusions: if he is in a mountainous country, he is enabled to trace, without much difficulty, the lowest and the highest elevation at which a particular species is found; and the nature of the soil, which may be considered the food of the plant, is at once known. But these advantages do not attend the zoologist: his business is with numerous functions in secret; while of the marine tribes he can never hope to be facquainted with more than a very insignificant portion. The following observations must, therefore, be considered as merely an outline of those general laws which seem to regulate the geography of animals.

The distribution of animals on the face of the globe must be considered under two heads, general and particular. The first relates to families or groups inhabiting particular zones, and to others by which they are represented in another hemisphere. The second refers to the local distribution of the animals of any particular country, or to that of individual species. It is to the general distribution of groups, as a celebrated writer has well observed, that the philosophic zoologist should first direct his attention, rather than to the locality of species. By studying nature in her higher groups, we discover that certain functions are developed under different forms, and we begin to discern something fof the great plan of providence in the creation of animals, and arrive at general results, which must be for ever hid from those who limit their views to the habitations of species, or to the local distribution of animals.

Animals, like plants, are generally found to be distributed in zones. Fabricius, in speaking of insects, divides the globe into eight climates, which he denominates the Indian, Egyptian, southern, Mediterranean, northern, oriental, occidental, and Alpine. In the first he includes the tropics; in the second, the northern region immediately adjacent ; in the third, the southern; in the fourth, the countries bordering on the Mediterranean Sea, including also Armenia and Media; in the fifth, the northern part of Asia, where the cold in winter is intense; in the seventh, North America, Japan, and China; and in the eighth, all those mountains whose summits are covered with eternal snow. It is, however, easy to perceive, that this, though a very ingenious, is a very artificial theory; the divisions are vague

and arbitrary, and we know that animals of one country differ essentially from those of another, although both may enjoy the same degree of temperature. M. Latreille has therefore attempted a more definite theory. His two primary divisions are the arctic and the antarctic climates, according to their situation above or below the equinoctial line; and taking 12° of latitude for each climate, he subdivides the whole into twelve. Beginning at 84° N. L., he has seven arctic climates: viz. the polar, subpolar, superior, intermediate, supratropical, tropical, equatorial: but his antarctic climates, as no land has been discovered below 50° S. L., amount only to five, beginning with the equatorial, and terminating with the superior. He proposes, also, a further division of subclimates, by means of certain meridian lines; separating thus the old world from the new, and subdividing the former into two great portions; an eastern, beginning with India; and a western, with Persia. He proposes, further, that each climate should be considered as having 24° of longitude and 12° of latitude. system certainly approximates more to what we see in nature than that proposed by Fabricius; yet Mr. Kirby observes with truth, that the division of the globe into climates by equivalent parallels and meridians wears the appearance of an artificial and arbitrary system, rather than of one according to

nature.

This

Mr. Swainson considers that the geographic distribution of animals is intimately connected with the limits of those grand and obvious sections into which the globe is divided; and that in proportion to the geographical proximity of one continent to another, so will be either the proportional identity or the analogy of their respective animals. He considers Europe, Asia, and Africa as agreeing more particularly, in possessing certain animals in common, which seem excluded altogether, from America and Australia; both of which are not only isolated in situation, but their animals have a difference of form and habit from those of the three continents of the old world. He considers that the animal geography of Asia is connected with that of Australia by the intervention of Borneo, New Guinea, and the neighbouring isles; while that of America unites with Europe towards the polar regions. These five great types or divisions will, of course, present certain affinities ar analogies dependent upon other causes, arising from temperature, food, and locality.

Vertebrated animals have a wider range than invertebrated animals, thus resembling man, who is spread over the whole earth: the dog and the crow are found wild in almost every climate; the swallow traverses, in a few days, from the temperate to the torrid zone; and numerous other birds annually perform long migrations. Next to these, insects, above all the other Invertebrate, enjoy the widest range; the house fly of America and of Europe are precisely the same; and Mr. Swainson has observed in Brazil vast flocks of butterflies, which annually migrate from the interior towards the coast.

Marine animals have, in general, a wider range than those strictly terrestrial. This may probably originate in their being more independent of the effects of temperature. It is remarkable, that, with the exception of the crow and two or three others, the land birds of America differ entirely from those of Europe, yet that nearly all our aquatic species are found both in the new world and in the southern coasts of Africa.

THREE-WHEELED ORRERY.

To the Editor.

SIR.-I inclose for insertion in your Magazine, a perspective view of the external arrangement of a three-wheeled orrery, which I invented during my residence in London, early in the year 1837.

The wheel-work, &c., is inclosed within a large circular frame of mahogany, of about eighteen inches in diameter, E E, on the upper surface of which is carefully laid down the signs of the ecliptic-the days of the month, and hours of the day, as delineated. The sun is represented by a ball, S, in the centre, gilded, and is six inches in diameter, to the right of which is a small terrestial globe, F, three inches in diameter, on which are engraven the several countries of the world, with circles of latitude and longitude, and is surrounded with a small engraven ecliptic circle, K, and circle of altitude, L. The ball, E, representing the earth, is inclined at an angle of about 234°, and is attached to an axle which ascends from the wheel-work, and by virtue of which connexion it preserves its parallelism in its circular journey round the sun, thereby familiarly exhibiting the cause of the change of the seasons, and different lengths of day and night throughout the year, &c. Immediately under the earth is fixed a small circular dial-plate, on which is engraven the twenty-four hours of day and night, which is very serviceable in attaining the time of terrestial phenomena. Under this dial-plate is another, which is stationary, and on which are engraven the days of the moon's age; and lastly, another circle is attached to the wheel-work, and on which is laid down the degrees, &c. of the nodes of the moon's orbit. This ring or circle is inclined at an angle of about 54° to the plane of the frame, E E. This ring has a retrograde motion in the ecliptic in the space of 18 years and 224 days, which is nearly the period of the nodes. Between the circles of the hour, at the foot of the earth's axis, and the circle of the moon's age, a horizontal arm extends from the wheel-work, and carries a perpendicular arm, H, which is partly hollow, for the purpose of affording a vertical motion suitable to the moon's declination, &c. M is a small ball of about three-quarters of an inch in diameter, and is furnished with a black cap, which exactly covers from view one-half of the lunar globe, and to which is attached a kind of forked arm extending upwards, and has a connexion with the sun through the medium of the slight horizontal bar, W, and joined to the sun at I. In short, with this very simple orrery, the following very interesting astronomical phenomena may be distinctly ascertained, and which, so far as I know, is the first time such important results from such simple causes have been effected :

Phenomena exhibited by the New Orrery. 1.-The unequal lengths of day and night during the year, and hence the cause of the vicissitude of the seasons.

2. The sun's place in the ecliptic, declination, &c. 3. The periodic and synodic revolution of the moon. 4.-The moon's diurnal rotation on its axis. 5.-The age and phases of the moon. 6. The motion of the moon's orbit. 7.-The motion of the apogee of moon's orbit. 8.-The eclipses of the sun, moon, &c.

All the above being effected by a very peculiar arrangement of only three wheels and a pinion. I may add that the moon goes round the earth in the ma

chine in 29 days, 12 hours, 44 minutes, 25 seconds, and round its own axis in the same time. The earth is moved by hand, is assumed to perform its journey round the sun in 365 days, 5 hours, 48 minutes, and 9 seconds. The moon's orbit makes a retrograde movement through all the signs and degrees of the great ecliptic circle in 6,798 days, 8 hours, and that of the apogee in 3,231 days, 18 hours, tropical time.

I generally exhibit this simple orrery in my astronomical lectures, and as it gives general satisfaction, and as a number wish to have copies of its form, I send it to you, in order that they may see it engraved in your widely-circulated Magazine, of which I have been a subscriber since its commencement. I may, at some future period, render you a description of the wheel-work of this instrument, as also of a variety of original and various astronomical machinery, should the present be acceptable to your readers.

E. HENDERSON.

IMPROVEMENT OF THE DAGUERREOTYPE.

THE process of Mr. Wolcroft, an American, patented in England by Mr. Beard, for quickening the action of the Daguerreotype, so as to produce the effect in a few seconds, is now carried into practice at the Polytechnic Institution in taking likenesses. The room fitted up for the purpose is at the top of the building in Cavendish-square. The roof is composed for the most part of large sheets of plate-glass, stained blue to soften the light, and this glass roofing traverses so as to meet the rays of the sun at any part of the day. The sitter is placed on an elevated platform, with a support for the head, and the camera obscura rests on a shelf a few feet distance from him. The construction of the camera itself, as thus applied, consti. tutes part of Mr. Woleroft's patent. Instead of using a lens to refract the rays of light to a focus, he employs a reflector, about seven inches diameter. By this means a much greater number of the rays issuing from the object are concentrated within a given space than could be otherwise accomplished, and the image is consequently the brighter. The speculum may also be placed nearer to catch the rays of light than a lens, and this also affords an additional increase of collected rays in the image. The silvered plate, prepared with a coating of the vapors produced by iodine mixed with nitric acid, or with bromine, so as to quicken the action of the light, is put into the focus of the reflecting mirror. The person whose likeness is to be taken keeps his face steady for a few seconds, and the effect on the iodine coating is produced. The plate is then taken away, and excluded carefully from the light until it has been exposed to the vapor of mercury, which attaches to the parts acted on by the light, and the image becomes visible-a perfect fac-simile of nature. Before the plate is exposed to the light, the iodine is washed off, and all further change is thus prevented by exposure. The time occupied by the process varies with the intensity of the light. Some likenesses were taken in five seconds, others occupied twenty, according as the sky was clear or clouded. The difficulty experienced, is to determine the exact time that the plate should remain exposed to the vapor of mercury, the requisite time is at present determined only by trial, and the judgment of the operator. It must therefore require some practice to produce the best possible effects.