:

is easily moveable on the rod, and the other is connected with the rod or one end is fixed to a support, and the upper end of the pendulum is attached to the other the arrangement being such that when the spiral rod expands or contracts, it raises or depresses the bob on the pendulum rod, or raises or depresses the pendulum itself through the fork: the effect being a practical shortening or lengthening of the pendulum exactly to the extent that the change of temperature has lengthened or shortened the pendulum rod; the acting length of the latter, therefore, never alters. In applying this principle to the watch or chronometer, the spiral spring and the compensator are made of the very same material and dimensions: and it is so arranged that, when change of temperature alters the length of the spiral spring, the same change alters that of the compensator which acts on the "regulator;" and thus the length of the acting part of the spiral spring is kept without change.

IMPROVEMENT IN THE SAFETY VALVE.-Without an effective and reliable safety-valve, the use of a steam-boiler must be constantly attended with the most imminent danger, Whatever care may be bestowed by the manufacturer on the construction of the safety-valve, it may be rendered nugatory by the ignorance or temerity of the person in charge of the engine: since he may overload the valve, and thus create a pressure within the boiler which it was not constructed to endure, and which it may not be capable of bearing. The evil may indeed be prevented by the use of two safety-valves, one of which is beyond the power of the engine man. But ingenuity has devised a still more simple remedy; one that not only prevents the production of steam at too high a pressure, but which actually causes every attempt to produce it to be accompanied by a reduction of pressure, and thus removes all temptation to tamper with the valve. The new form of safety-valve differs little from the ordinary kind, and is extremely simple. In the ordinary kind the fulcrum of the lever is absolutely immovable: in the new kind, it is fixed; in ordinary circumstances, being kept down by a spiral spring. But attempting to overload the valve brings the lever down on a stud, which is at the side of the valve most remote from the fulcrum, and which comes into action as a new fulcrum by supporting the lever, changing the latter from the third to the first order. The former fulcrum yields to the additional weight, the spiral spring being compressed, and is raised up, the safety-valve being at the same time opened, or allowed to open; and thus the steam is permitted to escape, though at a pressure too small to raise the valve when weighted as it should be. In its normal state the fulcrum of the lever is at one end, the weight at the other, and the power that is the tendency of the safety-valve to rise-between the fulcrum and weight. When the valve is overloaded, the weight-that is the resistance of the spiral spring is at one end, the power-that is the weight with which the lever is loaded-is at the other, and the fulcrum-that is the stud on which the lever has been brought down by the overloading-is between the power and weight: the effect of the latter being aided by the tendency of the steam to raise the valve.

A NEW GLASS FOR OPTICAL PURPOSES.-The density imparted by

thallium, as illustrated in thallic alcohol, suggested the application of that metal to the production of a very dense, and therefore highly refractive glass; and experiments made on the subject have been extremely successful. Difficulties of a serious character were encountered at first, the glass produced being fibrous, and not very transparent; but these have been overcome by the assistance of M. Feil, a glass manufacturer of great experience, and a thallic glass in every respect suited to optical purposes has been obtained. When carbonate of thallium is employed in its manufacture, its tinge is yellowish; but if this is considered an objection, the substitution of sulphate for the carbonate affords a perfectly colourless result. Thallic glass is the most dense, and the most highly refractive and dispersive known.

MAGNETISM AND DIAMAGNETISM OF GASES AND VAPOURS.-A simple and effective experiment by which the magnetism and diamagnetism of gases and vapours may be rendered visible to a large audience has long been sought for, and has at length been discovered. It consists in blowing a bubble at the end of the stem of a clay tobacco-pipe, the gas used for inflation being oxygen, and the fluid a solution of soap mixed with glycerine, which affords a bubble that lasts a considerable time. The bubble is placed above the poles of an electro-magnet, and at very small distance from them. When a current is sent through the coil of the electro-magnet the bubble is attracted, and if the circuit is completed and broken several times in succession, a very striking oscillation of the bubble will be produced. If magnesium is burned over the pole of an electro-magnet to which a conical form has been given, when the circuit is complete, the smoke will be divided laterally, and assume the form of the letter U.

LITERARY NOTICES.

THE CONSTELLATION-SEASONS: An Easy Guide to a Knowledge of the Stars. Exhibiting, in Twelve Planispheres, the Appearance of the Heavens at any Hour of the Night, all the Year round. By RICHARD A. PROCTOR, B.A., F.R.A.S. (Longmans.)-Mr. Proctor has produced one of the most useful series of maps we have seen for the purpose he had in view, namely, enabling students to learn the position of the chief stars and constellations at various periods of the year, or to recognize them at any time. "Each map," he tells "contains the whole of the visible heavens at the hour and date mentioned beneath it; the centre of the map is the point over the observer's head at the time named; the outline of the map is the observer's horizon; each star is placed in its proper direction as respects the compass-points (marked in round the map); and each star is placed at its true proportionate distance from the centre." For the teaching of young people, and for adults who wish to know the position of particular stars at certain dates, these maps will be

us,

found very handy. Mr. Proctor has devoted great labour to their production, and he deserves the sincere thanks of all who wish to see the elementary facts of stellar astronomy simplified. They will be of important value to amateur telescopists.

A HANDY BOOK TO THE COLLECTION AND PREPARATION OF FRESH WATER AND MARINE ALGE, DIATOMS, DESMIDS, FUNGI, LICHENS, AND MOSSES, AND OTHER OF THE LOWER CRYPTOGAMIA, WITH INSTRUCTIONS FOR THE FORMATION OF AN HERBARIUM. By JOHANN NAVE. Translated and Edited by the Rev. W. W. SPICER, M.A., F.R.M.S. (Hardwicke.)—This is really what it calls itself, a " Handy Book," with twenty-six plates, and elaborate directions for collecting and preserving the objects to which it alludes. It will be found of much use to beginners. The information is conveyed in a very clear and simple manner.

A TREATISE ON PUNCTUATION, AND ON OTHER MATTERS RELATING TO CORRECT WRITING AND PRINTING. By an OLD PRINTER. (Pitman.) -Good punctuation is an immense aid to the intelligibility of a book, and many works of merit are quite puzzling to read for the first time, because their punctuation has not been made upon a good system. The little book before us is well conceived and judiciously executed. We recommend it to all who desire to learn a simple but necessary art.

NOTES AND MEMORANDA.

NEPTUNE'S GROTTO.-Under this title some ingenious person has brought out a pretty chemical toy, which we saw in operation at Messrs. Horne and Thornthwaite's. A white solid is put into a clear solution, and thereupon beautiful arborescent and other forms are seen to grow in the course of a few minutes. If the experiment is performed on a small scale in a little zoophyte trough, under the microscope, and viewed by reflected light, with a 14-inch objective, the effect is singularly beautiful. A chemist will easily recognize the materials employed. They give rise to a double decomposition, and the precipitation in crystalline form of an insoluble salt of lead.

VOLCANIC ACTION IN THE AZORES.-M. St. Claire Deville read to the French Academy a letter, dated Angra, June 7, 1867, published in the journal “ A Persuaso," at St. Michel, in the Azores, stating that, from May 26, they had experienced strong earthquakes, and that in the night of June 1-2, a volcanic vent was formed nine miles north-west of Serreta, which continued active, and occupied a zone of more than 2 miles in a westerly direction. The writer states, "It was in the sea, lat. 38° 52', and long. west of Greenwich 27° 52′, in a line from Tercera to Gracioza. It constantly emits great stones and enormous masses of lava, the accumulation of which may produce a new islet, likely to be dangerous. Jets of vapour and boiling water appear in different positions, and for a considerable distance a strong odour of sulphur is noticeable. From time to time noises are heard like repeated discharges of artillery. The Intendant of the Marine, various civil and military engineers, and others, have gone off to survey these phenomena, but the danger has kept them at a considerable distance.

MEDICINES THROUGH THE NOSE.-M. Raimbert recounts to the French Academy various experiments in administering medicines in the form of a snuff, to act by absorption through the membrane of the nose. Sugar powdered with hydrochlorate of morphia, and taken in this way, he found useful in violent

headache. He mixed five centigrammes of the morphia with two grammes of powdered sugar, and in some cases strengthened the dose. He thinks digitalis, nux vomica or strychnine, iodide of potassium, calomel, etc., may be administered with advantage in this way.

THE LEPORIDES.-Some time ago there was a good deal of talk about the leporides, or crosses between hares and rabbits, that were alleged to be raised in considerable quantities by an enterprising Frenchman. Dr. Pigeaux, writing in the "Bulletin de la Societé Imperial Zoologique d'Acclimation," observes, “To sum up, therefore, we would affirm that leporides exist, undoubtedly, under both forms, with predominance of the hare or of the rabbit; but as a species, or even as a variety, we cannot admit them, since, like all other crosses, they have only an accidental productiveness." He adds that their flesh has neither the whiteness of the rabbit nor the flavour of the hare.

COAL-FIELDS OF BRAZIL.-A paper read before the Geological Society shows the existence of large coal-fields in the province of St. Catherine's, Brazil. The coal is found to be of good quality, and its profitable working will depend on facilities for transport.

METEORIC APPEARANCES ON JUNE 11.-We have received the following from Mr. D. A. Freeman :-"It was stated in the 'Gazzata Ticinese' of June 20, that in several of the Swiss cantons, at Basle, at Zurich, at San Gall, at Geneva, there was observed on June 11, at 9 p.m., the sky being serene, a meteor of great splendour, which for an hour showed remarkable changes, and terminated by assuming the appearance of a small cloud."-[From the "Opinione," published at Florence, June 23.] We find in " Comptes Rendus," June 17, the following letter from M. Silbermann, referring to a remarkable meteor seen by him about the same time:"Thursday, June 11, at 8.10 p.m., a shooting star, more brilliant than the finest of 13th November last, passed a little north of the zenith, moving with extreme slowness from the west to the north-east. I reckoned that it took two seconds and a half to traverse an arc of about 20 degrees. Before becoming extinct it manifested a remarkable recrudescence of splendour, shooting forth yellowish green sparks. Before the last instant it was exactly like a fusée d'artifice, burning with white fire. M. Louft at Palaiseau, and M. Auzou at St. Aubin d'Ecroville (Eure), inform me that they noticed the same facts." In "Comptes Rendus," June 24, M. Bonnafont states:-"On the 11th of this month, at 8 to 8.15 (about), I was sitting in my garden at Antony, near Paris, when towards the north a splendid meteor appeared. Its form appeared to resemble an enormous Congreve rocket (fusée a là Congreve), with a red incandescent point in front. Immediately afterwards this body exhibited a very brilliant yellowwhite colour, like a hood, over two-thirds or less of its length, from which streamed an incandescent, hairy train, leaving considerable traces in the atmosphere. M. Barba, engineer of the Imperial Marine, studying the points I indicated to him, was able to lay down its exact trajectory. At the moment the bolide appeared to me, it was N. 3° E. of the meridian of Paris, and 22° 30 above the horizon. It then described a parabolic curve, with the convexity towards the zenith, and constantly approaching the horizon, disappeared in a few seconds behind my house, at 34° N.E. Its height above the horizon was then 16°."