Page images
PDF
EPUB

Paris, has been engaged in examining the improvement which might be effected by replacing the crown glass, and at last confidently recommends rock crystal for this purpose; by the use of which, he says, he can, with the same magnifying power, augment the light, and diminish the length of the telescope, without much increasing the price of the instrument.

By comparing the best telescopes of Dollond, made in 1758, of three and a half inches aperture and forty-two inches focal length, with what may be obtained by using rock crystal instead of crown glass, he concludes that the length may be shortened to twenty-eight inches three lines, and even to twenty-five inches, by the use of Guinand's glass, at the same time that the same magnifying power is obtained, and the clearness or quantity of light augmented. In terrestrial telescopes, a still greater reduction than this may be effected, amounting even to one half the whole length, and one eighth of the diameter.

The hardness of rock crystal, although it will make more work necessary, will, at the same time, secure the telescope from injury, as it will always replace the external glass; and so, whilst it resists itself, the wear and tear of use will protect the soft glass within. As to the difficulty of obtaining pieces of sufficient size, M. Cauchoix thinks that, when a demand is created for them, they will be found and brought into the market. He has actually constructed an instrument of thirty lines clear aperture and eighteen inches long, which has been substituted with great advantage for another of twenty lines in aperture, and equal length attached to a theodolite. Stars are seen by the former, which were invisible with the latter. He has also constructed a great number of smaller size, many of which having been tried both on land and at sea, have been found equally efficient with ordinary telescopes of double their length. -Ann. de l'Industrie, ii. 34.

3. Zenneck's Pycnoscope, or Instrument to measure the Density of Solid Bodies. The instrument consists of a cylindrical glass vessel, surmounted by a plate and a graduated glass tube. The cylinder must be six or seven times larger in diameter than the tube, and is to be closed above by a ground flat plate of glass or metal, which may be applied to the edges of the cylinder with pomatum, so as to render the junction perfectly air and water tight. This plate has a hole in the centre to receive the tube, which is also to fit accurately. A ring or plate of lead is also to be provided, to be put upon the plate, and prevent it from rising when the apparatus is filled with water. A glass vessel or flask is to accompany this apparatus, competent to hold an equal quantity of water with the cylinder. When this instrument is to be used, the substance, whose specific gravity is to be examined, is to be put into the dry pycnoscope, its weight ascertained, and then the measure of water poured in. The height to which this rises in the graduated tube, shews the volume

of the body under examination; which, with the weight, gives the specific gravity.-Kastner's Archives, xiv. 81.

4. Method of preparing Flax at Goldkronach, in Bavaria.Successive layers, an inch in thickness, of straw, beech ashes, and flax which has been hackled once, are put into a tub or other vessel; the different layers being separated by cloths. The whole is covered over with a double cloth; and upon that, a layer of ashes, a handbreadth in thickness. This arrangement is to be watered every twelve hours, at first with cold water, which, some time after, is to be drawn off, and again used. The waterings are to be repeated twelve times, and the temperature raised each time— the three last applications being with boiling liquor. After the twelfth time, the flax is to be left for twelve hours in the solution; after which, the vessel, and its contents, is to be taken to running water, the flax carefully washed, beaten on a flat stone with a mallet having a large surface, re-washed, pressed, and then passed through a solution of black soap. It is to be dried in a quiet, shady place; being spread out in thin layers upon canvass, and moved from time to time until dry. It is to be beaten again with the mallet, and then hackled to the degree required. Experience has proved that, by this means, the roughest and most friable flax becomes as soft as silk. The whole operation consists in a careful application of an alkaline lye, which, dissolving out the gummy and resinous matter, removes that which had rendered the fibres brittle, and makes them, in consequence, both finer and softer. -Bull. Univ., D. x. 279.

[ocr errors]

5. Alloyed Iron Plate.-A manufacture of prepared iron has been practised, and the substance produced used, to a considerable degree, in Paris. The object has been to prepare iron in large plates, and other forms, so that it will not rust; and this has been effected by coating it with an alloy of tin and much lead, so as to form an imitation of tin plate. The trials made with this article have been favourable; it very well resists the action of certain fluids that would rapidly corrode iron alone, and can be prepared of any size, and at a low price. Its use in the manufacture of sugar pans and boilers, in the construction of roofs and gutters, is expected to be very considerable.-Bull. d'Encouragement.

6. Cohesion of Iron and Steel.-According to the experiments of M. de Mittis, a bar of good Styrian iron, one inch square, was broken by a weight of 400 quintals; a similar bar of Styrian steel, not hardened, was broken by a weight of 749.53 quintals; a third and similar bar of the meteoric steel, from the manufactory of M. Fischer, at Hainfeld, in Austria, was broken by a weight of 1130 quintals. Kastner's Archives, xiv. 175.

7. Fire Arms.-It is proposed by M. Burel to fix a small mirror, 0.47 of an inch, in the side, near the mouth of the piece, so that the person using it shall see the reflection of his own eye. In this way it is supposed that very exact aim may be taken; and the experiments made by various officers and sportsmen seem to encourage the idea that this application may be useful. It is considered as most likely to prove serviceable when applied to war pistols.-Bull. d'Encouragement.

8. Preparation of Hydraulic Lime. It was observed by M. Lafaye, and confirmed by M. Vicat, that lime which had been slaked by immersion, may be preserved for a long time without alteration.

MM. Ollivier, assisted by M. Vicat, have succeeded in preparing a lime which they can preserve for a long time in sacks, without losing any of its properties, and at the same price with unslaked lime. The use of this lime is said to be very advantageous; it avoids any difficulty in the measurement, and is more easy of transference. Its use in preparing walls for fresco painting, is superior to all other lime.

It is sold in very fine powder; and, having been sifted, is free from vitreous particles. These operations, as well as the moving it into the sacks, is not at all inconvenient to the workmen, who continue for twelve hours per day thus occupied, without injury. From one to one and a half millions of sacks of this lime are sold annually, being principally employed in the construction of canals in Bretague.-Bull. d'Encouragement.

9. On Hydraulic Cements.-A paper is contained in the JernKontorets Annaler of Sweden, for 1824, on hydraulic cements, by M. Pasch, who gives in it an account of the experiments that had been made at the Canal de Goetha. After many experiments upon the substances which most importantly improved lime by mixture with it, he concluded that the most powerful was an aluminous schist. It would be difficult to find a lime, he says, which would not be improved by mixture with this schist. For application it is to be burnt and then reduced to powder: although the carriage to a distance makes this preparation expensive, yet its good qualities are supposed fully to compensate.

No good effect was found to be produced by the use of manganese in any way; nor by the use of trap rock, green-stone, calcined granite powder, or ochre.

Relative to lime-stones those are not the best which are purest, but the reverse. A considerable quantity of argillaceous earth in limestone makes the cement formed with it set well in water; on the contrary, siliceous earth gives greater hardness to the mortar, but it does not then so well resist water. Bituminous limestones

were found to be the best, perhaps, because those used were mingled with aluminous schist. The cement made with this stone set in a few minutes, and soon acquired the hardness of stone, to such a degree, that the substance might be used in place of Parker's cement. Bull. Univ. E. x. 343.

[blocks in formation]

The Cathedral at Strasburg

142.

The Steeple of St Stephen, at Vienne, (Austria)
The Steeple of St. Martin, at Landshut

138

137

St. Peter's, at Rome....

132

130.5

119

109.7

109.4

109

107

105

101.6

79

The Steeple of St. Michael, at Hamboro'
The Steeple of St. Peter, at Hamboro'
St. Paul's Cathedral, at London.....
The Cathedral of Ulm

The Cathedral of Milan

The Tower of the Asinelli, at Bologna
The Dome of the Invalids, at Paris
The Cathedral of Magdebourg...

The Cupola of the Pantheon, at Paris
The Balustrade of Notre Dame, at Paris

The metre is 39.37 inches.-Bull. Univ. F. xv. 257.

66

11. Prevention of Fires in Theatres.--In consequence of the frequent occurrence of fires in theatres, particular precautions have been taken with the theatre of the Port St. Martin, at Paris. A thick wall of hewn stone separates the audience part from the scenic part of the house; all the doors in it are of iron, and may be shut instantly, in case of fire; finally, the insulation of the spectators from the stage is made perfect by means of a screen of plates of iron, which falls down before the stage. This screen, which weighs between 1,200 and 1,300 pounds, is easily worked by two men, and slides up and down upon guides, so as readily to take its place. Besides these precautions, reservoirs of water are established in the roof, which may be connected, when necessary, with vessels of compressed air, and made to throw a powerful jet over a very large part of the building.-Moniteur. Bull. Univ. E. x. 333.

12. Influence of Metals on the Motion of magnetised Bodies, &c.— Whilst experimenting upon the extraordinary effect of metals upon magnets, discovered by M. Arago, M. Seebeck observed, amongst a number of other effects, now well known to the public, that if a magnetic needle be suspended horizontally above a metallic plate, and made to oscillate, not in the ordinary way, but as a pendulum, still the same influence of the plate beneath will be exerted upon it as in the usual experiment, and the number of oscillations will be

fewer than if no metal plate had been there. He also observed, that, if a copper pendulum be made to vibrate above a magnet, or between its poles, the vibrations are less in number and extent than if no magnetic influence had existed in the immediate neighbourhood of the pendulum. Amongst metals mercury is that which, as a pendulum, is least acted upon by the magnetic influence. A pendulum of wood, with a ball of marble or glass, is not at all acted upon or influenced by the magnetism either of magnets or of the earth.-Annalen der Physik, 1828, p. 352.

Query. What will be effect of the earth's magnetism upon pendulums vibrating in different directions relative to the magnetic meridian, and in different latitudes upon the earth's surface?-Ed..

[ocr errors]

13. Diurnal Variations of the Barometer.-M. Bouvard bas lately read a paper to the Academy of Sciences, of Paris, on the diurnal variations of the barometer. The following are the results of his observations. i. Towards the equinoxes the barometer attains its maximum at 50 minutes past 8 o'clock A.M., and at about 11 o'clock P.M. The minimum at the same period of the year is at 4 o'clock A.M. and at 4 o'clock P.M. ii. In summer the maximum is at 10 minutes past 8 o'clock A.M. and in winter at half-past 9 o'clock A.M. The other particular periods of the barometer vary equally with the seasons. iii. The day periods are longer than those of the night, and their variations are nearly like the corresponding periods. iv. Under the equator, and at the level of the sea, these periods are at their maximum. v. Under the equator, at very elevated situations, these periods diminish like the corresponding temperatures, and nearly as the square of the cosine of the latitude. According to M. Bouvard, these results will require conformation by new observations, made with the best instruments in high latitudes, and in very elevated situations under the equator,

14. Theory of Light.-If by means of a lens, a concave mirror, or a cylindrical glass, rays emanating from a luminous point or line are made to converge; and if two parallel surfaces, from which the polish has been slightly removed, are introduced into the converging pencil, coloured rings or bands are produced in the focus, which arise from the interference of the rays transmitted by the first surface, and dispersed by the second, with the rays dispersed at the first passage, and afterwards transmitted regularly. M. Babinet has communicated to the French Academy of Sciences some formulæ for every case which experiment affords; and in the second part of his memoir on the subject, has suggested considerations which lead to the formulæ of coloured rings of the thick plates of Newton, the theory of which had been already pointed out by Dr. Young. Several very extended notes also relate to, 1. The author's method of calculating the interferences by the versed sines of very small angles, which give immediately the differences of the paths described by the rays. 2. A simple demonstration of the

« PreviousContinue »