Scientific.

New Zealand Mail, Issue 209, 11 September 1875, Page 5

Scientific.

At the usual meeting of the Philosophical Society on Monday night the discussion on Mr. Carruthers paper was brought to a conclusion. Mr. Travers read a paper on the period at which the moa became extinct. Mr. Travers combatted the theories of Dr. Uaast on this matter, and brought forward certain recent evidence that had come to his knowledge in support of his statements.

M. Saree, a Professor, Neufchatel, has, says the Revue Scientificuc, found out a plan for keeping, eggs. Whilst they are fresh he coats them with paraffin, and they are said to keep without any. trace of change for two years.— London Medical Record.

Those who are interested in the Arctic Expedition will like to know that Sir Charles Wheatstone has invented for the use of the expedition an instrument for telling the time in the dark, which will he very welcome in the long Northern winter. The invention is due to some adaptation of the polarization of light.

The sjieed of trains in Germany is given by a recent report as follows Greatest speed per hour, including stops for express and fast trains, 34 miles ; for ordinary passenger trains; 25.. Slowest speed were for express and fast trains 21 miles per hour ; ordinary passenger trains, 1(J miles. Average speeds per hour, for express and fast trains, 2S miles ; for ordinary passenger trains, 21 miles.

An English paper says:—“The process recently discovered whereby glass is so toughened as to be made almost unbreakable throws considerable light on some passages in classical writers hitherto believed to be devoid of truth. Mr. F. A. Raley mentions the following anecdote, for instance, hitherto discredited, but which may now be fairly believed. It is given in Dr. Smith’s Dictionary of Greek and Roman Antiquities’ (art. Vitrum): —‘A strange story with regard to an alleged invention of malleable glass is found in Petronius (and elsewhere.) An artist appeared before Tiberius with a cup of glass. This he dashed violently upon the ground. When taken up it was neither broken nor cracked, but dinted like a piece of metal. The man then produced a mallet, and hammered it back into its original shape.’ This account would now seem to be verified beyond the possibility of doubt, if we allow of some exaggeration, or perhaps confusion, between the flexibility of glass and its tough and unbreakable texture.” Many of our readers may have noticed the unusual appearance of illustrations in The Times in the shape of the small charts which have been appended to the daily weather reports since the Ist May. This measure has been the long-postponed carrying out of the line of action indicated by the Meteorological Committee in their report for last year, and the chart in its present form differs’but little from that printed as a specimen in that report. The method of preparation of that chart seems simple enough at present, but it had been the fruit of much thought, as the problem of producing, in the space of an hour, a stereotype fit for use in a Walter machine has not been solved without many and troublesome experiments. In the first place, a material had to be provided which would admit of being engraved rapidly without burr or chipping, and would without further preparation serve as a mould for type metal. Secondly, drill pantagraphs had to be adapted to engrave the lines, and to lie furnished with a guage, so as to vary their depth at pleasure. The actual process is as follows :—The outline of the line is kept standing, and the composition is run in a mould hearing the outline on one face. The block, which is now au outline a chart of the British Islands, is then placed under the pantagraph drill, which reduces the original drawing, furnished from the Meteorological Office, to one-fourth. The barograms and wind-arrows are put on direct from the drawing, the figures and words by means of templates, in order to insure uniformity in the type. The instant the block is engraved it is ready to be stereotyped, aud then it is a simple matter to adapt it in the usual manner to the cylinder of the machine. The initiative in this new method of weather illustrations is due to Mr. Francis Galton, and the practical details have been carried out by .Messrs. Shanks and Johnson, of the Patent Type Founding Company. It is hardly necessary to allude to the value of such charts as these as a means of leading the public to gain some idea of the laws which govern our weather changes. As soon as they appear in our afternoon papers, we may hope for a more intelligent comprehension of the difficulties which beset any attempt to foretell the weather of these islands for the space of even twenty-four hours. We may safely say that with these charts we have not seen the end of weather illustration, which was set on foot more than four years ago by Sir W. Mitchell

m the Shipping Gazette, and lias been continued daily; but, whatever improvements may hereafter he introduced in the process, it must be remembered that the credit of breaking the egg is due to the gentleman wo have named. POLISHING WOOD. A correspondent of the Boston (US.) Cabinet Maker given the following details of the methods of polishing wood : . I "’LI first describe the method of polishing pianos that is used in all first-class factories. I lie same process will answer for any other piece of furniture by merely substituting for the scraping, where scraping is not practicable, a fiiling, properly colored. First, give the work three coats of scraping, or No. 2 furniture varnish, allowing each coat to become perfectly hard before applying the next ; then scrape ofE the varnish with a steel scraper, properly sharpened on au oil-stone, and in scraping be careful not to cut into the wood, but merely remove the varnish from the surface, leaving the poles filled, Smooth with No. 1 sand paper,_ and the work will be ready for the polishing varnish, four coats of which must he put on, allowing each coat to harden. To determine the proper time required for the hardening, I would say that one coat will not lie ready for the next until it is so hard that you cannot make any impression on it with your thumbnail. The four coats having been put on, and the work having stood a few days—and the longer the better—rub down with fine-ground pumice-stone and water, applied with a woollen rag. The work must he rubbed until all lumps and marks of the brush are removed ; wash off with a sponge, and dry_with a chamois-skin ; let the work stand out in the open air for a day or two, taking it into the shop at night. The work should now receiv e two coats more of polishing \ arnish and a second rubbing, after which it is ready for polishing. I urniture may be polished after the first rubbing, and in that case the polishing is performed with lump rotten-stone and water applied with a woollen rag. Put plenty of rotten-stone on your work, with water enough to make it work easy. Rub until all marks aud scratches are removed. Rub the rotten-stone off with your bare hand, keeping the work wet. What cannot be removed with the hand should be washed off with a sponge. After drying with a chamois-skin, bring up the polish with the palm of your hand, moving it lightly and quickly, with a circular motion, over the work. Glean up the work with a piece of soft cotton, dipped into sweet oil, and lightly touch all the white spots and marks of the rotten-stone. Remove the oil with wheat flour, applied with soft cotton, and finally dust off with a soft raf or silk handkerchief.

Hie following method is known as the Shellac or 1; reach polish. In preparing for this process, add to one pint of shellac varnish two tablespoonfuls of boiled oil ; the two to be thoroughly mixed. If you want the work dark, add a little burnt umber ; or you can give the work any desired shade by mixing with the shellac the proper pigment in the dry state. Apply the shellac thus prepared with a small bunch of rags held between your fingers. In applying it be particular in getting it on smooth and even, leaving no thick places or blotches. Repeat the process continually, until the grain is filled, and the work has received sufficient body. Let it stand a few hours to harden, and then rub your work lightly with pumice-stone and oil, applied with a rag. A very little rubbing is required, and this is to be followed by the cleaning of the work with rags as dry as possible. With a piece of muslin wet with alcohol go over the work two or three times, for the purpose of killing the oil. Have ready jib. of pure gum shellac dissolved in one pint of 1)5 per cent, alcohol. With this saturate a pad made of soft cotton, covered with white muslin, and with the pad thus formed go over your work two or three times. To become proficient in this work, practice and close attention are required. SAW SHARPENING AND SETTING. (From the Ewjlisk Mechanic.) Although machines have been contrived by means of which the gullet-teeth of circular and other large saws can he ground on an artificial emery-wheel, yet such appliances fail when employed for saws and angular teeth ; so that hitherto the sawyer has had to depend chiefly on his file and on his manual skill. To sharpen a saw to cut well, it should he clamped between two parallel strips of wood nearly as long as the saw, the whole being firmly retained between the jaws of a bench vice. Should the saw be a bow-saw, it must bo removed from its frame previous to being set. in all cases the strips of wood should clench the blade so near the teeth as only just to allow of the play of the file between them. 1 I lings being thus adjusted, a three-square file, known as a saw file, is chosen and removed, pro tempore, from its handle. In order to ensure equality in the length of the teeth, the file, hold parallel to the blade of the saw, is passed along the tops of the teeth for a few times.

Ihe operator then proceeds to sharpen tooth No, 1 nearest to him, which he does by working the file crosswise in the groove before the first tooth, keeping the file nearly level, but slightly pointing to his right shoulder. In the same manner lie sharpens the 3rd, sth, 7th, &c., always skipping one till he arrives at the end of the saw. Ho then removes his saw from the vices, and proceeds to place it in the contrary direction. Again he takes the file in his hand, and operates on the remaining teeth, viz.,. 2nd, 4th, Oth, &c. In this inode the cutting edges of the teeth are alternately sharpened.

But were the saw employed in that state, it would be found to bind or cling to the work in a most tiresome manner, owing to the “ kerf,” or width of cut, being the same as the thickness of the blade of the saw, the latter therefore finding much resistance in its passage through the cut portions. To remedy this

defect the saw requires “setting,” and to effect this every alternative tooth is slightly bent out of the straight line in opposite directions. Sawmakcrs set their saws by striking the alternate teeth with a narrow-headed hammer on a smooth anvil, to which a proper inclination is given ; then turning the saw over, the untouched teeth are bent in the ojqmsite direction. This is undoubtedly the best mode of setting a saw, but sawyers generally who are not sawmakcrs are content with bending the alternate teeth in contrary directions with a slotted steel plate, somewhat resembling a key with wards. Several contrivances have lately been brought forward under the name of patent saw-sets, by means of which the amount of bend given to each tooth becomes a fixed and invariable quantity. If a saw be properly set, a needle placed between the first teeth will run from end to end on tilting the saw.