in addition to the excentric wheel apparatus, the press might be used in the common way, when the engine moving-power was not in use.

It may be proper to state the supposed rate of execution of the press I have described. The shaft for the extentric wheel is supposed to revolve once in two seconds, and the wheel of the rack-work once in each second, and that eight revolutions complete the operation of inking. The time necessary to run the coffin into the press two seconds, and the same time to run it out. Then,

The time of inking, during which also the sheet is taken out, and a white one placed in the tympan, is

8"

One impression in 14 seconds gives 256 in the hour.

In the Sketch, the outer coffin, or carriage of the tympan, is supposed to consist of three sides, and without a bottom, and made very thick in the sides for strength. Perhaps it would be better to be made with a bottom, in which case, the winter and range, so far as the tympan carriage has to be moved, must be as much lower than the range for the inking table as the bottom is thick, that the forme may be on the same level as the inking table.

EDINBURGH, Feb. 22. 1831.

Note by Mr FRASER.

SINCE the paper referred to by Mr Clerk Maxwell appeared in the last Number of this Journal, it has been satisfactory to learn, that the subject had been also attracting considerable attention elsewhere. Among other commu nications received, we have been favoured with one from Mr Cowper, and another from Mr Napier, the patentees of the two large printing machines formerly alluded to. The latter gentleman states, that he has already secured a patent for machinery, part of which, although in some degree differing from that preposed by us, is intended for the same purpose, but that he has not yet brought it to perfection; and Mr Cowper says, that his patent for the large machines includes also the application of the inking-apparatus to the common presses, but that he has declined to make such an application, though frequently requested to do so, from a belief that the printer would derive no good from it.

We have also had the pleasure of conversing with Mr Cowper junior, who mentioned that, when lately at Paris, he saw the self-inking apparatus actually attached to the common press, and at work, in the Royal Printing-office there; but that the inking-apparatus was ultimately abandoned, in consequence of the unforeseen obstacle in pulling, which it is one particular object of Mr Clerk Maxwell's invention to remove. Were this part of the latter gentleman's improvement also to be carried into practical effect, not only would equality of colour by the self-inking apparatus be obtained, but also a no less important desideratum be supplied-equality of pressure by steam-power. At present very great muscular exertion is in general required to produce good work, even with very powerful presses; and, therefore, should one or both of the pressmen be unable, or find it difficult, to take a sufficiently strong pull, several devices are apt to be resorted to for lessening the labour, such as drowning, instead of merely damping, the paper, increasing the soft substance between it and the point of pressure, applying too much ink, &c., but in all of which cases, however sharp and new the type may be, nothing but a very irregular, blurred, or blunt impression is produced. Hence it will be obvious, that were the means of obtaining a steady, regular, and more or less powerful pressure by steam-power at the common press once procured, it would essentially contribute to the beauty of typography; and hence will likewise be perceived the very great importance of this part of the plan now proposed.

It is curious that, on the other side of the Atlantic, the application of a self-inking apparatus to the common printing press has at the same era been thought of, and carried into effect. In the number of the Christian Instructor for February last, it is stated, that an American Journal, speaking of the improvement in printing, remarks, that "the introduction of the Napier machine into this country, together with the Treadwell press, made at Boston, has been the means of producing quite a revolution in printing. A great variety of machine presses have subsequently been invented here, and the self-inking apparatus has been improved and applied to the common press.” "The most rapid machines can be made to strike 5000 impressions in an hour. This is equal to the work of twenty hand presses; or, to express it differently, it will enable us to print the common 18mo Bibles at the rate of 75 copies an hour. A hundred presses at this rate, could supply every family on the earth with a Bible in three years."

For the printing of publications having a large circulation, it has always been obvious that the machines possess a decided superiority over the common presses; but work of this kind is wholly confined to large towns, and even in these to comparatively few printing-offices. By far the greatest proportion of the printing business everywhere consists of work of a miscellaneous nature, and of which comparatively few copies are required. On this account very few printers, indeed, could keep a single machine in constant employ. ment, even were it otherwise applicable to such work, which, neither for ge neral economy nor for very fine work, it is universally admitted not to be. Besides, six good presses can be obtained for the price of one machine, and the great majority of printers throughout the kingdom have seldom or never occasion for so many. These, too, can be applied to a variety of purposes at the same time, and one or more only be used as circumstances may require.

Should a press be at any time unemployed, there is comparatively little loss, for the first cost is not great, and there are no men's wages to pay in the interim; but the very reverse is the case with a printing machine, the original outlay for one, independently of that for the engine, &c., being from L. 400 to L. 700, and a considerable subsequent expense of keeping in repair, and a stated rate of wages to one man and two boys at least. Hence it is evident that common presses must of necessity continue to be in much more general use than printing machines, and could Mr Clerk Maxwell's ingenious improvement upon the presses be carried into effect, there is no doubt of their value and utility being very greatly increased. By it, not only would the labour of one man at each press be entirely saved, but that of the other be also reduced to little more than supplying the sheets of paper. The quality of the work, too, from the regularity of inking and pressure, would be much improved, and means would undoubtedly soon be fallen upon for increasing or diminishing the quantity, in a given time, according to the nature of the work in hand. There would certainly be the additional expense attendant upon an engine, &c. for each printing office, which there is not at present: but surely if the same kind of mechanical power be found more economical and advantageous than manual labour for coffee-grinding, and similar purposes, it would be much more so if it could be rendered applicable to the important operations of miscellaneous letter-press printing. In short, it is very evident that the demand for printing presses and self-inking apparatuses of the kind contemplated would be every where very great, and would soon amply remunerate any one, whether in Europe or in America, who might be so fortunate as to bring them first into effective and economical operation.

Account of a Platina Lamp. By GEORGE MERRYWEATHER, Esq. of Whitby. In a Letter to Professor Jameson. (With a Plate.) *

A FEW years ago, Sir Humphry Davy made the discovery, that, if a coil of small platina wire be placed around the wick of a spirit lamp, and rendered red-hot, the wire would continue ignited for a length of time, after the flame was blown out. In consequence of having lately witnessed this singular phenomenon at Professor Hope's lectures, and that it was generally viewed as nothing more than an amusing experiment, I was induced to give the subject some attention, as I felt convinced that a mode might be devised of turning it to some useful purpose.

On the 3d of last month, I contrived an apparatus; but not meeting with the success I expected with platina wire, I made use of spongy platina, which I found to answer the object. I had in view. In order that a correct idea may be formed, I have made a drawing of this apparatus. The lower part is con

structed of tin, in the body of which is the reservoir, large enough to contain a quart of alcohol; the bottom of the interior of the reservoir is concave, in order that the cotton-wick may take up the last drop of the spirit. After the wick has been spread in the form of a coronet at the top of the lamp, the platina wire cage, containing one piece of spongy platina, is to be pricked into the centre of the wick, and to be kept nearly in contact, but not to touch it. After the reservoir has been filled with alcohol, the wick is to be inflamed, and a minute afterwards, the spongy platina will have become incandescent, when the flame is to be suddenly blown out, and the glass cover to be immediately placed over the platina. Without any further care or attention, the platina ball will keep ignited for thirteen or fourteen days and nights. A similar apparatus has been kept ignited for this period in the University of this city. If a tube is connected with a reservoir (containing a sufficient quantity of alcohol), and the bottom of the reservoir of the lamp, I have no hesitation in saying that the platina ball may be kept ignited for years, as the spongy platina does not appear to be in the least deteriorated by being kept in a state of constant ignition.

I had a similar lamp made, on a small scale, to keep ignited from eight to ten hours, which affords sufficient light to shew the face of a watch in the dark of night. It causes no annoyance from a glare of light. If a light is required, the glass cover is to be elevated, and the platina, gently touched with a match of oxy-muriate of potassa, which will be instantly inflamed; and it is no small recommendation, that there is not the least danger to be apprehended from fire.

There have been two objections to this lamp, which were formidable ones, namely, the expense of the alcohol, and the odour which is diffused through the apartment in which it is placed. As a remedy for the first, I find by experiment, that equal parts of alcohol and whisky answer quite as well as pure alcohol; or every one-third of alcohol and two-thirds of whisky do very well, which I find, on calculation, to cost about one penny for eight hours. As a remedy for the second objection, I have contrived an apparatus for condensing the vapour, of which I have made a drawing. In order that it may be correctly understood, I have represented it as transparent; but the apparatus is made of tin, which is to be suspended from a nail in the wall, Fig. 4, G. The glass tube of the lamp is to be inserted into the tin tube of the condensing apparatus, which will completely destroy the strong odour of the vapour. The liquid is drawn off by the stop-cock at the side of the condenser, which will be found a compound of water, acetic acid, and some other peculiar ingredients given to it by the platina.

We may add, that this lamp may prove very useful in all mining districts, as a constant light that may be depended upon, if the reservoir is periodically replenished. If this should be the result, I shall feel myself amply repaid for all the pains I have taken.

EDINBURGH, March 5. 1831.

Explanation of Figure of Platina Lamp in Plate V.

Fig. 3. A, Vent for the vapour. B, Glass cover. C, Platina ball. D, Cotton wick. E, Holes for admission of air. F, Reservoir.

Observations on the Fossil Trees of Van Diemen's Land. By WILLIAM NICOL, Esq. Lecturer on Natural Philosophy*.

DEAR SIR,

In compliance with your request, I now give you the result of the examination I have made of the specimens of fossil wood you have lately received from your friend Colonel Lindsay, at present in New Holland +.

Thin transverse sections of each were formed on the method I have adopted, and which I have described minutely in a work lately published by Mr Witham on the Structure of Fossil Wood. On viewing these sections, by help of a microscope, or even a common pocket lens, it is sufficiently obvious that five of the specimens belong to the family of Coniferæ, and two to the tribe of true Dicotyledons. Four of the coniferæ are common woodstone, the fifth is wood-opal. One of the dicotyledonous specimens is wood-stone, and shews the organic structure throughout the whole mass; but the other specimen, which is in the state of opal, shews the organic structure only in certain parts of the mass. In such parts, there is a peculiarity which I do not recollect to have seen in any other specimen of petrified wood; and which is, that the pores or vessels, instead of being filled with petrifying matter, are perfectly empty. Throughout the greatest part of this magnificent specimen, the vascular struc

* Read to the Wernerian Society, 5th March 1831.

† In examining the structure of petrified woods, it has been the practice to shew it either by simply cutting and polishing the surface, and examining it by reflected light, or by cutting thin slices, and examining them by transmitted light. This latter, although the best mode, has hitherto afforded less satisfactory results than it ought to have done, owing to the imperfection of the cutting and polishing process. Mr Nicol, after much labour, has succeeded in so perfecting this process, as to enable us by it to shew, in an elegant and beautiful manner, the most minute structures of fossil, and also of recent vegetables. The plates in Mr Witham's book on "Fossil Trees," shew what may be effected by this process. We doubt not that it will also be generally used by botanists in their examination of the structure of recent woods; for, as well remarked by Mr Nicol, this structure may afford means of arrangement of plants hitherto but little attended to. We have always maintained that the internal structure of plants might, to a certain extent, afford the means of scientific arrangement of the groups of the vegetable kingdom.-EDIT.

JANUARY-MARCH 1831.

A a