ternal elevation of these cylinders; and fig. 2 a vertical section through the centre of the apparatus. A and B are the cylinders, which are mounted on a hollow basement, C, which is separated into two compartments by the partition D. H H are two upright standards, stepped in the bottom of the basement C, which carry three guide rings, II I, placed at equal distances apart, a plan of one of which rings is given separately in fig. 3. L L are two open spirit holders,

Fig. 3.

attached to the top of the uprights H H, consisting of two concentric chambers, the outer one being much smaller than the inner. K K K K are lengths of cotton thread, such as is used for wicks of lamps, which are drawn through rings fixed at the bottom of the smaller of the spirit holders LL, till the two ends meet at an equal distance from the rings; the ends are then turned over the edges of the spirit holder, and drawn through the holes M M, in the guide rings II I, reaching at bottom to a little way below the undermost ring. N N are two circular cups, which surround the bottoms of the uprights H H, and communicate with one another by the horizontal pipe O. P is a force pump, the induction valve of which opens into the pipe O. Q is a pipe which leads from the force pump to the top of the cylinders, where it communicates by lateral branches with two close spirit reservoirs R R, which have no other communication with the rest of the apparatus, except through the connecting pipes S S, and vent tubes TT. Such being the construction of the apparatus, let us suppose that the spiral holders L L are filled with alcohol to a little way above the level of the under termination of the vent tubes T T, and that the reservoirs R R are also partially filled with the same. The alcohol is drawn up, by the capillary attraction of the cotton threads K K, out of the holders L L, and passes down those portions of them which are suspended in the cylinders, keeping them constantly wet, and presenting large alcoholic surfaces, possessing great affinity for

807

any aqueous vapours which may come in contact with them. The alcohol which drops from the cotton threads is collected in the cups N N; and when it has accumulated there in a sufficient quantity, it is pumped up by the force pump P into the close reservoirs R R, whence it flows down the pipes S S, until the holders L L are again filled to the level of the lower ends of the air tubes T T. And as often as the alcohol in the holder L L falls below the level of the air tubes T T, the air rushes up into the reservoirs R R, and forces down a quantity of spirit sufficient to raise the surface of the liquid in L L again above the level of the lower ends of the air pipes T T. UU are float valves, the spindles of which are encased in glass tubes, by which the height of the alcohol in the close reservoirs R R, and consequently in the open holders, can always be ascertained by inspection. The gas to be subjected to the action of the alcohol is first admitted into the cylinder A through the pipe E, and ascending to the top of that cylinder, flows through a passage, F, in the entablature, into the cylinder B, descending which, it passes off into the main by the pipe G. In making this circuit, any aqueous vapour which may happen to be still suspended in it, is almost certain to be absorbed by the alcohol with which it comes in contact; and should any portion of the alcohol itself become vaporized, and pass off in combination with the gas, it can only tend to increase its illuminating powers. V V are doors by which admission is ob-. tained to the inside of the cylinders, in order to adjust or renew the threads from time to time. These doors are fixed by means of the pinching screws W W, which are screwed into the bridges X X, which abut against the doors on the outside, and are inserted at their ends into lugs, Y Y, projecting from the sides of the cylinders."

ANASTATIC PRINTING.

Falmouth, April 25, 1845. Sir,-In the year 1836, I introduced a process for the transferring of copperplate engravings (by the old masters) as well as letter-press printing, &c., to stone, zink, tin, pewter, type-metal, fusible metal, lead, copper, glass, &c., and had impressions taken from each, but the original subjects were destroyed by the chemical agents used. Since that time I have succeeded in transferring prints and letter-press without even soiling the originals, fixing the same on metal, wood, or paper, and printing from the form any

number of copies. The process is so faithful in its operation, that the finest line of the etching needle is preserved. Facsimiles of the Illustrated News, Pictorial Times, copper and steel-plate engravings, wood-cuts, letter-press, &c., may be produced in 30 minutes after publication. Yesterday I took an impression from the Meg Merrilies" of last week's Illustrated News, and I defy the most critical eye to detect the copy-the shades of ink and lines being as perfect as in the original.

66

That the art of "Anastatic printing" was known long before it received that name, or acquired its recent notoriety, we can of our own personal knowledge testify. About four or five years ago, Mr. Jobbins, the wellknown Lithographer, of Warwick-court, Holborn, showed us a fac-simile of a page. of a printed work which he had obtained by this means, and which was as perfect a production of the sort as any we have since seen. At the Royal Institution last week, this new art formed the subject of an interesting lecture by Professor Faraday, from the report given of which, in the Athenæum, we extract the following very lucid explanation, as well of the principles on which it depends, as of the mode in which it is practised.-ED. M. M.

Professor Faraday on Anastatic Printing.

Anastatic printing is the avάoraois (the fresh raising up) of copies from a printed sheet of paper. This, by the process described, may be done to an indefinite extent. The philosophy of this process and its practice were explained and exhibited. The philosophy of the Anastatic printing rests on a few known properties of the articles employed. Thus, water attracts water, and, oil, oil; though each mutually repels the other. Metals are much more easily wetted with oil than with water, but they will readily be moistened by a weak solution of gum; and, finally, this property, of their becoming wet by water, is greatly increased by phosphatic acid. To these properties of oil, water, and the metals, may be added, as one of the principles of the Anastatic printing, the readiness with which part of the ink

of any newly-printed book or engraving can be transferred by pressure to any smooth surface beneath. If, for example, a corner of a newspaper be fixed on a white sheet of paper, and then pressed, or rubbed with a paper-knife, the letters will be distinctly seen in reverse on the paper. This effect is known to bookbinders, and our readers may have seen, especially in the case of books bound soon after publication, pages disfigured by the "setting off," or transfer of the ink of the opposite page. Such being the properties of the matters concerned in Anastatic printing, the process is simple. The printed paper, whether letter-press or engraving, is first moistened with dilute nitric acid and then pressed with considerable force, by a roller, on a perfectly clean surface of zink. By this means every part of the sheet of paper is brought into contact with the plate of zink. The acid, with which the unprinted part of the paper is saturated, etches the metal, and the printed portion sets off on it in the manner already described, so that the zink surface presents a complete reverse-copy of the work. The principles before specified are now brought into operation. The zink plate, thus prepared, is washed with a solution of gum in weak phosphatic acid. This liquid is attracted by the etched surface, which it freely wets, while it is repelled by the oil of the ink in which the writing or drawing on the plate is traced. A leathern

roller, covered with ink, is then passed over the plate, when a converse effect ensues. The repulsion between the oil, ink, and the watery surface over which the roller passes, prevents any soiling of the unfigured parts of the zink plate, while the attraction between oil and oil, causes the ink to be distributed over the printed portions. In this condition the Anastatic plate is complete, and impressions are pulled from it by the common lithographic process.

Mr. Faraday concluded his description by stating, that when it was required to apply the Anastatic printing to very old originals, which do not set off their ink on pressure, the following expedient was resorted to. The page or print is soaked in a solution, first of potass, and then of tartaric acid. This produces a perfect diffusion of minute crystals of bi-tartrate of potass through the texture of the unprinted part of the paper. As this salt resists oil, the ink-roller may now be passed over the surface without transferring any of its contents, except to the printed parts. The tartrate is then washed out of the paper, and the operation proceeded with as before, commencing with the moistening by nitric acid.

NO. VI.

Let the radius A C be divided in G in such a manner, that A G shall be to C G, as 4r is to (3-4)r, and the point G thus determined will be the position of the centre of gravity of the revolving plane B A D, and AG is the radius of the circle G M N, described by the point G, while the plane revolves about the tangent E F as an axis. Since A G, the radius of the circle described by the point G, is represented by the expres(3π-4) r the circumference of that " 3п

sion

Here we have another instance of

the utility of considering the subject in this way, for we are not aware of the existence of any rule for calculating the solidity of a body of this form, and we believe it would puzzle the calculator to assign its contents by any other method. By the application of the centrobaric principle, however, we are enabled to discover the rule, and it rests with our readers to bring it into use, by applying it to the calculation of figures similarly constructed to the one we are now considering.

In our last paper, No. V., page 244, it was shown that the centre of gravity of the generating plane B A D is situated in the radius A C, which bisects the area, and distant from the centre at C by a space, of which the value is the

4r

13

3π

by the rules already laid down, the area of the revolving semicircle or generating πr2

plane is expressed by; and accord

2

ing to our general principle, as enunciated at page 35, vol. xlii., the solidity of the figure generated by its revolution, is equal to that of a prism whose base is the area of the plane, and altitude the circumference of the circle described by the centre of gravity; consequently, by multiplication, we have

π r2 ̧ 2r(3π—4) _ πr3 (3π − 4)

2

X

3

=

3 for the solidity of the figure whose section is B D A H I, and which is generated by the revolution of the plane BAD about the tangent E F. Let the expression just found be reduced to its lowest numerical value, and it becomes 5.680873; and from this expression we obtain the following practical rule, viz.

Multiply the cube or third power of the radius of the revolving plane by the constant coefficient 5.6808, and the product thence arising will be the solidity of the figure.

This is the rule as deduced from our formula in terms of the radius; and in order to transform it into another that shall be expressed in terms of the diameter, we have only to consider that the cube or third power of the diameter B D, is equal to eight times the cube of the radius A C; that is, 8 A C3-B D3. If, therefore, we substitute B D3 for 8 A C3, or 83 in the expression 5.6808 r3, we shall get 0-7101 B D3 for the solidity of the figure in terms of the diameter; and the practical rule, as deduced from this last form, is