193

MISCELLANEOUS INTELLIGENCE.

§ I. MECHANICAL SCIENCE.

1. Tulley's New Catadioptric Microscopes.-Mr. W. Tulley, stimu lated by the example and success of Amici, has invented a reflecting microscope, the optical principle of which is, we believe, entirely new and original; the objective part consists of an elliptic metal, and a perforated plane one of corresponding dimensions, forming an angle of forty-five degrees with it. A section of a cylinder is introduced into the hole of the plane metal, in such a way as to allow light to pass towards the elliptic metal, but to exclude it in every other direction, so that no false rays can enter.

The manner in which the instrument operates is as follows:The object to be viewed is placed nearly whole in the plane, through which its rays diverge towards the elliptic metal, from which they are reverberated to the plane metal, which reflects them at right angles to the eye-piece, by which the image they form is viewed in the usual way (the object of the section of the cylinder is to exclude false light). This instrument has its good and evil properties, like all others. It has been duly executed by Mr. Tulley, and may be considered in its optical principle and its performance, equal to that of Professor Amici, over which, indeed, it possesses the advantage of being capable of receiving an unlimited angle of aperture. The objection to it is that the diagonal metal does not permit the approach of an object to the focus of the elliptic one, with the facility necessary for practical purposes. Only very small objects can be viewed, which must be mounted in a particular manner, having to be introduced as it were into the external part of the hole in the plane, where no latitude of motion can take place; sliders, aquatic live boxes, &c. are wholly inadmissible: these defects, will we are afraid, confine this instrument to the cabinets of the curious. There is a great difficulty in executing the plane metal, for that part immediately about the hole must be perfect, and the sharp edges of the aperture are a great obstacle to correct execution (which, however, has been conquered by Mr. T.). There are impediments also in the adjustment of the plane, which is apt to lose its figure, being made as thin as possible to admit the approach of the object to it.

The other microscope forms its image by one reflection only. Opaque objects are mounted upon a small arm, and presented to the focus of an elliptic metal inserted at the end of a tube, at the other extremity of which the usual eye-glasses are placed, while the illumination is effected from an aperture in its side.

Transparent objects are illuminated by means of light, furnished by a small plane metal placed diagonally behind them, being in fact exactly similar to that which is employed in the Amician

JULY-SEPT. 1828.

microscope, to co-operate in forming the image, but which is here used only as an illuminator, being removed beyond the focus of the concave metal.

Any Amician instrument may, of course, be easily modified into this form, for it will be merely necessary to draw its plane metal further back, and to perforate a fresh hole in the side of the tube to admit the light, with some additional contrivance to present the object in its proper place. This reflector, considered only with reference to its optical principle and performance, is at once the most simple and the most perfect of the whole family of compound microscopes, but has nearly the same inconveniences as the other, relative to the application of objects. To those who regard not the difficulty at which they procure perfect vision, this instrument must be highly valuable, and probably will long retain a place among microscopes as a verificator or proof engiscope; for there can be no doubt that the vision it affords is of the purest and most unadulterated nature.

2. Carpenter's Aplanatic Solar Microscope.-This is the first solar instrument which has ever possessed achromatic object-glasses regularly worked to correct diverging rays. The experiment of converting telescopic object-glasses of short foci to the purpose of forming an image for the solar microscope has been often made, but of course without any good effect; it is as rational to expect that such glasses should answer both for divergent and parallel light, as that the same medicine should cure a diabetes and a dropsy. The pictures of microscopic objects given by the present instrument are totally freed both from chromatic and spherical aberration, and in consequence of which the coloured fringe which forms the outline of all objects shown with common object glasses is removed, together with that nebulous indistinctness which causes the image to appear a mere shadow when inspected closely, and, therefore, fit to be viewed only from afar.

The observer may boldly proceed up to the very screen on which the picture is formed by the achromatic glasses, and will find that the image instead of losing by this close scrutiny developes those minute details which were invisible at a distance. But it is chiefly when opaque objects are viewed that the incontestable superiority of the achromatic shines forth in all its splendour (especially if contrasted with the effects of common glasses, which, it is well known, give an image of radiant bodies, which is a mere jumble of aberration of both kinds, not fit for public exhibition.)

Those who fancy that aplanatic glasses are no better adapted to the nature of a solar microscope than to that of a camera-obscura, would do well to examine Mr. C.'s instrument; in fact the public voice has already decided the question,

The frame of this instrument is on a gigantic scale, the illuminating lens being a foot in diameter, with everything else in proportion,

The immense body of light condensed together by it gives a wonderful richness and vivacity of colouring to the image which, combined with its sharply-defined outline and vast dilatation, distends the faculties with surprise and pleasure, frequently surpassing the most lively anticipation.

Upon the whole there would be nothing to wish for or to find fault with about Mr. C.'s instrument if it possessed aplanatic objectglasses of sufficiently short foci to develope the tissue of animalcules and other regular microscopic objects. Nothing certainly can exceed the perfection of its combined double treble achromatic, the power of which is also admirably adapted for exhibiting large popular objects, but far too low to show those curious and difficult minutia which gratify a connoisseur. Such an objective as that famous deep sextuple one lately worked by Mr. W. Tulley, which demonstrates the most difficult test objects with such incomparable facility, would complete the effectiveness of this really respectable and scientific engine of public instruction and amusement. This deficiency is shortly to be supplied.

3. Improvement in the Barometer.-An improvement has been made in the barometer of Gay-Lussac by M. Bunten, which has been submitted to, and received the approbation of, the Academy of Sciences at Paris. Its object is to prevent the introduction of bubbles of air, which almost inevitably takes place when the barometer is carried either on foot or horseback, or in a carriage, in a horizontal position. It consists in expanding the glass in one part of the wide tube, so as to form it into a chamber, from the centre of which a capillary tube of a certain length descends perpendicularly, by which the mercury must necessarily pass, either when rising or falling. If a bubble of air enters, it necessarily moves up by the surface of the large tube, and is stopped at the top of the chamber, producing no error in the observation made whilst it is there. When the barometer is inverted the bubble escapes of itself. This invention, the reporters observe, does away with the only inconvenience attending the use of Gay-Lussac's barometers, without adding anything to their fragility.-Revue Ency. xxxviii, 536.

4. Effect of the Moon upon Barometric Pressure.-M. Flaugergues has added his efforts to those of the persons who have endeavoured to ascertain the effect of the moon's attraction upon the atmosphere of our globe, endeavouring to elucidate the subject by a very close and continued series of barometrical observations made daily at mid-day since 1808. The column of mercury in the barometer was 2.46 lines in diameter, and in the cistern 37.89 lines in diameter. The height was marked off to the th of a line, and corrections made for capillarity, variations of the external level, temperature of the mercury both in the tube and in the cistern. The following is the table of the mean height of the mercury drawn 02

D

up from daily observations from 19th October 1808 to 18th October 1827, a period of nineteen years. The observations were made in the observatory at Viviers, 2° 20' 55."5 longitude east of Paris, and 44° 29' 1" north latitude. The basin of the barometer was 56.78 metres (186.3 feet) above the level of the Mediterranean. Mid-day was chosen for the time of observation, because the height of the barometer is not sensibly affected at that time by the sun.

Number of
Observations.

6915....

Mean height in
millimeters.

755.44

Lunar positions.

General mean height

New moon or conjunction

234.

755.39

First octant...

First quadrature

Second octant. . .

Full moon or opposition.

Third octant

Second quadrature

Fourth octant

Northern lunistice

Southern lunistice

Lunar Perigee

Lunar Apogee.

The conclusions drawn by M. Flaugergues are-1. That the barometer rises from the second octant when it is lowest, to the second quadrature when it is highest, and then again descends to the first point: the total variation is 1.67 millimeters (.0657 of an inch). Thus in a lunar day, the barometer is lowest when the moon is 135° from the meridian towards the east; i. e., 9 hours 183 minutes of mean time before its passage across the meridian, or 6 hours 12 minutes after its passage. 2. The action of the moon is stronger when its declination is southern than when it is northern, contrary to the theory of Laplace. 3. The difference between the actions of the moon at the apogee and perigee, is 1.1 millimeter of the latter greater than the former. The author finally concludes that the number of rainy days is greater when the barometric pressure is diminished than when it is augmented.—Bib. Univ., Dec. 1827.

5.-On the Arrangement of Water Pipes in Streets.-The effect of temperature upon iron pipes, used for the conveyance of water, and also some other circumstances have been investigated by M. Girard: he has arrived at the following conclusions. 1. According to the effect produced by change of season and temperature upon pipes of this metal placed in subterraneous galleries, they altered in length for each centesimal degree (1.8 degrees of Fahr.), 0.0000985, a quantity about less than it would have been if they had not been confined on their supports by friction. 2. Although this effect is less when the pipes are put in the ground, it is still sufficient to occasion rupture, leakages, and other unpleasant accidents. 3. If the

joints are not made by bolts, but one end of a pipe is inserted into the mouth of the next pipe, then the space for the interposed substance should be as small as possible, and the substance one which swells when in contact with water. 4. The length of the joints should be considerable, both to prevent the escape of water and the flexure of the system of tubes. 5. To ensure tightness, the stuffing should be confined between a ring fixed to the end of the pipe, and a moveable ring sliding on the tubes. 6. That this precaution may be dispensed with by laying the pipes down in the coldest part of the season. 7. That pipes put into the ground should be supported at intervals by firm props of masonry, to prevent those inflexions which otherwise occur, and form ruptures. 8. That in large towns it is advantageous to place these pipes in subterraneous galleries, either such as are made on purpose, or else in the sewers. 9. That galleries have been tried advantageously for 20 years, and therefore should be resorted to, that those derangements of the pavement and inundations from broken pipes which are consequent upon the ordinary mode of proceeding, may, from henceforth, be avoided.— Globe, April 16, 1828.

6.-New Razor Straps.-A new kind of razor strap, invented by M. Ferrot, has received the name of euthegone. From the flexibility of leather, a round edge is given to the blade, for which reason paper is used in the new strap. Two kinds of very fine paper have been manufactured purposely, with fine and homogeneous pulp, mixed in the one case with fine emery, and in the other with very fine rouge. These papers are then steeped in melted tallow, afterwards pressed to give them a smooth surface, and then cut into bands, and mounted on pieces of wood properly shaped. Each strap has therefore two faces, one gray, on which the razor may be rendered very sharp, and the other red, which, polishing the edge, renders it extremely smooth. The razor must be laid very flat upon these straps-they improve by a few days use. When ineffectual from age, the surface should be rubbed with a very smooth piece of pumice, or with a little pumice powder on marble or ground glass; being then wiped with a piece of cloth, they are brought to their first state.-Bull. Soc. Encouragement.

7.- On the Fusion of Tallow.-The Council of Health at Nantes has been engaged in an investigation of the best means of fusing tallow, so as to avoid the injury and annoyance which arises from an abundant liberation of vapours, when the ordinary method is used. Much pains has been taken in acquiring all the information possible, and numerous experiments have been made both on a large and small scale. The best process which the Council has instituted appears to consist in using, according to M. D'Arcet's suggestion, a certain proportion of sulphuric acid, and operating in close vessels. By the use of the acid, the fumes always evolved. are very much altered and ameliorated in quality, at the same time