fore from the common kind only in being non-poisonous. The other variety of match is a very beautiful invention. It is called the safety match, and well deserves its name. In our last number (page 522), we gave a short notice of this invention, and we will therefore only briefly refer to it here. The oxidizing material alone is put upon the match, the red phosphorus being mixed with emery, and pasted on the side of the box; the match is therefore not a match until it is brought in contact with this friction-paper, and the splints may consequently be trampled upon and littered about the house with perfect impunity. No accidental ignition can possibly take place.

We have thus briefly sketched a few of the valuable applications of substances which some years ago were looked upon as utterly valueless. Coal-tar, rags, and bones, rise from the sewer and dust-heap, and are transformed by chemistry into costly luxuries, or necessaries of civilization, giving employment in their transformations to a large number of our working classes. Necessary limitation of our space has compelled us to omit all reference to other waste products which are now almost as extensively utilized; but an attentive examination of the magnificent and unrivalled display of chemical manufactures now collected together at South Kensington, will convince the student, that to the chemist there is no such thing as a waste product, that which is so designated being to him a coffer of untold wealth, ready to yield up its treasures to any one applying to it the master-key of knowledge.

No. IV.

THE PHILOSOPHICAL INSTRUMENTS.

BY JAMES BREEN, F.R.A.S.

INCE the Exhibition of 1851, the improvements in philosophical instruments have been sufficiently various and important. Those which are now universally known were then undreamt of. The stereoscope has come into general use, and instead of the ghastly representations given by the daguerreotype process, we have now solidity itself pictured forth in plain black and white by the assistance of this little instrument. The collodion process, with which it has been accompanied, has reached the utmost perfection. Photographs of the solar spots

have been taken as it were in relief,-transferred by electrometallurgy to a solid form, and, dispensing altogether with the engraver's aid, printed from in the ordinary manner. The binocular microscope has given a fresh impetus to the study of nature in its most minute and intricate forms. Telescopes, indeed, there were in abundance, and good ones too, at the last Exhibition, but they have since been exceeded in power and excellence, although, with the exception of Foucault's successful contrivance of silvering a parabolic glass surface, nothing novel has been introduced in their construction. In the matter of reflecting telescopes with metal mirrors, the movement has been retrograde; but even this, perhaps, has been judicious. At the epoch of the Exhibition of 1851, Lord Rosse's six-foot reflector was in full operation-disclosing the wonderful spiral structure of several nebulæ, resolving others, and thus connecting them, in different respects, with the form and nature of our own Milky Way. But the labour of years bestowed upon its construction, and the difficulty of keeping its polished surface in proper condition, have not been found sufficiently fruitful in results to warrant the extension of this description of telescope. Only one telescope of large dimensions has since been constructed on this plan,-the four-foot mirror of Mr. Lassell, from which, doubtless, by aid of the clear sky of Malta and the long experience of the maker and observer, great results may be anticipated. It is remarkable, that it has been the makers of reflecting telescopes who have been most successful in celestial discovery, the two Herschels, Lord Rosse, Mason, and Lassell, are striking instances of this, but the care required to keep them in working order, already alluded to, has caused astronomers to have recourse once more to the original refracting telescope, and the latter has gained considerably by the preference. Separate instruments for meridional observation (on a large scale) do not figure at the Exhibition of 1862. Thanks to the present Astronomer Royal, the transit instrument and mural circle have been united into one solid apparatus, with which a single observer can do the same work much more satisfactorily than two on the old system, and register the right ascension and declination of an object with the same ease and equal certainty as on the ancient plan.

The electric telegraph is now a domestic institution, vastly simplified, but yet capable of further improvement, particularly in the insulating of the submarine cable; for out of 14,000 miles already laid down, only 4,000 are stated to be in working order. It would be impossible, within the limits of a short summary such as the present, to go seriatim through the various objects exhibited by one hundred and fifty different inventors and manufacturers. In those articles where taste and ornamenta

tion are most in vogue, such as opera-glasses and optical toys, the British collection is as showy, and, we believe, much more solid than those of other countries. It is interesting to notice the most ordinary applications of science; how some dozens of spectacle-glasses are ground and polished at the same timearranged and fixed around a convex or concave disc,—and how a rough lump of steel is punched and worked, until, without joint or soldering, it comes forth a spider-web frame for those lenses, such as Ariel might give, or Cinderella receive. In the higher branches of optical art, where the brain is equally potent with the fingers, we miss many names familiar in 1851. Merz, of Munich, who gained the council medal at the last Exhibition, is not represented in the present building, although, from the fine collection of telescopes which he is now constructing, he might easily have spared a specimen. Ertel, to whom, for his fine graduations, the jury awarded the great medal in 1851, but who, nevertheless, by a decision of the council of chairmen, only received the ordinary one, is equally invisible. Troughton and Simms, to whom the same thing happened, are also unrepresented; and the names of Lerebours, Secretan, and Steinheil, do not appear in the catalogue. Only one specimen of Foucault's mirrors, and this of small dimensions, appears at the present international show. The United States, which, on the last occasion, contributed so much that was new and interesting-methods of recording transits, electric telegraph apparatus, photographs of the moon-do not send a single article to classes 13, 14, or 15, and yet the excellence of Alvan Clarke's telescopes is duly appreciated in this country. Neither the large telescope of Professor Amici (Florence), of 17 inches aperture, nor any other of the splendid list of his scientific instruments given in the catalogue, arrived, although they had been eagerly expected, at the International Exhibition.

Still, however, enough has been exhibited to show the progress of science during the last ten years. The large equatorial made by Grubb, of Dublin, strikes us by the solidity and convenience of its fittings; the diameter of the object-glass is twelve inches, and, should it be worthy of the mounting, will certainly make a noble instrument. The mere metal-work is, however, a subsidiary affair in a telescope-what is most required is perfect and colourless definition, and this is only to be attained by the purity of the glass and the accurate form and complete polish which the artist bestows upon the four spherical surfaces of the crown and flint lenses. The finish of Cooke's instruments is well known. His principal one is a telescope of eight inches aperture, equatorially mounted and furnished with a very solid base. The conveniences for motion in right ascension and declination are excellent; the hour circle is moved by

clockwork, which, as he is also an exhibitor in the department of Horology, may be expected to be perfect. This apparatus, whilst in motion, keeps the telescope always pointed to the same celestial object. The other telescopes which he exhibits are smaller, but the fittings and brass-work are in all cases very fine. Dallmeyer exhibits some astronomical telescopes in which the stand and slow-motion apparatus are very commodious. Wandering about the cases in the gallery, we perceive many fine telescopes of from one to five foot focus, and fixed on stands of all descriptions-nothing novel in design, although perfect in manufacture. Of the object-glasses (which are not exposed to view) we can form no opinion; but, considering their small size and the consequent ease with which they are made, it is almost certain that they are in all respects equal to the instruments of which they constitute so important a part.

The gem of the Exhibition, in this department, is the great 28-foot telescope belonging to J. Buckingham, Esq., C.E., who has fitted it up for his own private use, and has himself devised and manufactured all its various and novel machinery. The object-glass of twenty inches aperture is the largest successful attempt that has hitherto been effected. It is the work of Wray, and has been ground and polished to the true curves by his improved methods; speaking admirably for the perfection of the system, as the surface does not show the least grain when examined with a microscope, and the chromatic and spherical aberrations are quite corrected. Whilst amateurs and observers have worked their own mirrors with one surface, it has been reserved for opticians proper to produce the perfect object-glass of four or even six surfaces. Few can conceive the difficulty of producing an achromatic lens of twenty inches diameter the slightest deflection from the true figure, produced by an extra stroke of the polisher, renders the glass quite worthless. It may be stated that the most powerful refractor hitherto in use (if we except that made, during the present year, by Alvan Clark, of 18 inches) is the 16-inch, by Merz, at Pulkowa; but the light-grasping power of this latter (varying as the squares of the diameter) is only as 256 to 400, in comparison with that here exhibited; so that when the present instrument is brought into operation, we may expect many discoveries to be made in the constitution of those faint nebula which Lord Rosse has rendered celebrated. This telescope has as yet been comparatively untried, but it is to be hoped that the vast amount of skill, labour, and capital employed in its construction will lead to many important results. The method of mounting is very commodious-all the clamping and slow motions can be effected from the eye end, and the

declination circle is intended to be read off from the same part. In the same case in the gallery in which this great object-glass is exhibited, there are other specimens of lenses, also ground and polished by Wray, all of which (including a 9-inch and 5-inch glass) have been equatorially mounted by Mr. Buckingham for his particular use. The simplicity and steadiness of the portable stand, and the beautiful workmanship of the 7-foot telescope, will be much admired. We may congratulate Messrs. Buckingham and Wray upon their remarkable success in this branch of optics, and upon the introduction into England of a perfection in telescopes, both as regards size and capability, which had hitherto been monopolized by the Munich artists.

The difficulty of obtaining a fixed position, either for an observer or his instrument, on board a rolling ship, has often been endeavoured to be rectified, but hitherto without success. Chairs, suspended like a chronometer in numerous gymbals, have not been found sufficient to give the necessary steadiness. Peg-tops, with a plane mirror on the upper part, spun on the deck of a ship, have been used in order to give a fixed horizon. Professor Smyth has turned the gyroscope, or rather the principle of free rotation, to account in an instrument constructed by him, and tried with success on his journey between Leith and St. Petersburg. With this gigantic instrument, which required to be set in motion by the combined action of all hands on board ship, he was enabled to keep an instrument directed to any heavenly body notwithstanding the rolling or pitching of the vessel. The utility of this invention will be readily understood by those who have endeavoured to observe the occultation of a star or of Jupiter's satellites on the deck of a sailing or steam vessel. With a similar apparatus he is able to register the degree and effects of all those motions, or to show any two of them combined.

When Oersted perceived (in 1819) that a magnetic needle suspended freely could be turned to one side by the transmission of the electric fluid passing through a wire parallel and near it, no matter at what distance the battery was placed, the telegraph was virtually discovered. It took long years, however, to realize this invention; to find a fitting battery; a perfectly insulated wire; a convenient code of signals. During the few years previous to the Exhibition of 1851 this science made immense progress. Not only were telegraphs then transmitting messages, but actually printing them on ribbons of paper, and the electric current had even been used in recording the passage of a star across the wires of the transit-instrument; thus throwing the ear out of employment altogether, and bringing the sense of touch into operation instead. Since that time the principal endeavour has been to simplify the alphabet, to obtain