A similar structure

shaped extremities of the optic nerve. probably exists in all the Monoculi, and most of the inferior Crustacea. In the Daphnia the crystalline bodies are pearshaped, short, and few in number; such also is the case in Gammarus pulex. In all, the principal peculiarities, independent of the absence of facets on the cornea, consist in the anterior rounded extremities of the crystalline cones, and the manner in which they project anteriorly beyond the stratum of pigment in which their apices are immersed; to which, however, there are some approximations in insects. Are these peculiarities connected with the aquatic habits of these animals, rendering necessary a greater refractive power?

The

The pear-shaped masses in the Daphnia and Gammarus pulex present an approach to the lenses of simple eyes, as they occur (aggregated) in Oniscus, &c. The latter, however, besides possessing a spherical lens, have a round vitreous humour, and never the transparent conical masses. difference from these aggregates is still greater in Monoculus apus, the cones being elongated, small, and numerous. Hence. it becomes necessary to discriminate the compound eyes without facets, of the inferior crustacea, as well from the compound eyes with facets of insects and crustacea, as from the aggregates of simple eyes in Millipedes and Onisci.

Ueber den Bau der Augen bei Murex tritonis, Linn., vom Dr. J. Müller zu Bonu. (Meckel's Archiv, No. 3, 1829, On the Structure of the Eyes in Murex tritonis.)

THE

HE black points at the extremities of one of the pairs of feelers in Helix pomatia, were long ago described by Swammerdam as eyes, in which he recognised an aqueous humour and a crystalline lens. Subsequently, Stiebel ('Meckel's Archiv,' b. 5) examined the same parts in Helix pomatia and Cyclestoma viviparum, and found in them a choroid, an iris, and a crystalline. As the true nature of these supposed eyes of gasteropodous mollusca was, however, still by many considered problematical, Dr. Müller availed himself of an opportunity of deciding the question by examining them in Murex tritonis.

They are here placed at the outer side of the feeler, on a small eminence near its root, the axis of the organ being in the same direction as that of the feeler itself. The surface of the eye is convex, and surrounded by a prominent ridge formed.

by the substance of the feeler. The eye itself is easily separable from the surrounding substance, and is then seen as a blackish sphere, with its greatest diameter in the longitudinal direction. A thin transparent lamella, continuous with the substance of the feeler, is expanded in front of the globe of the eye. This cornea, as it may be considered, is separated from the globe by a space extending over its anterior third, which in the recent state is probably occupied by a fluid (aqueous humour).

The posterior part of the globe, embedded in the substance of the feeler, is formed by a greyish-black membrane (choroid), which at its anterior part forms a narrow circular belt of a darker colour (iris), perforated in its centre by a circular pupil. The external margin of the cornea reaches somewhat farther back than the outer edge of the iris.

The optic nerve, which is a branch of the nerve running in the axis of the feeler, perforates the posterior part of the cup formed by the choroid, and probably expands on its inner surface into a retina, of which some imperfect traces were visible. The inner surface of the choroid is perfectly black; its cavity is almost completely occupied by a firm, round, amber-coloured mass, similar to those found in the eyes of spiders, and representing either a crystalline lens or vitreous humour.

As the most essential parts of an eye are here present, and of comparatively large size, we are warranted in supposing that there must be a corresponding power of vision. Experimental observations on this point are the more desirable, as in Helix and Cyclostoma, where there is a similar organization, the animals appear not to see, or at least not distinguish objects.

FOREIGN AND MISCELLANEOUS INTELLIGENCE.

§ I.—MECHANICAL SCIENCE.

1. RESISTANCE OPPOSED TO WATER MOVING IN PIPES.(D'Aubuisson.)

NOTWITHSTANDING the endeavours made to deduce formulæ from experiments on the passage of water through tubes, so as to assist and guide the engineer in laying down pipes to supply manufactories or towns, yet frequent mistakes have occurred: thus at Paris, at the Fontaine des Innocens, only two-thirds of the water calculated upon were obtained; whilst, in the faubourg St. Victor, only the half of that expected issued from the pipes. These differences appear to result from experiments made on too small a scale, or with apertures disproportionate to the areas of the tubes; for the results of practice come sufficiently near to the formulæ of MM. Prony and Eytelwein, when the velocity of motion in a pipe was small in consequence of a contracted aperture made in a plate of metal being used. When the contracting plate was altogether removed, then the product in water was a fourth or third less than that given by the formulæ, from which M. D'Aubuisson concludes that the resistance increases with the velocity in a greater ratio than that given to it in the calculations; where it is supposed to increase proportionably as vm v, m being nearly equal to 0.055, and v representing the mean velocity.

In consequence of the arrangement and state of the water-pipes at Toulouse, some large and accurate experiments have been made there by MM. Castel and D'Aubuisson, in systems of pipes of 4.7 inches and 10.63 inches in diameter, and 1434 and 1986 feet in length. In these experiments the quantity of water passed and the pressure were varied; the results were noted, and also calculated by the formulæ, so as to deduce the loss of pressure due to the resistance of the pipes: that by calculation came out 27., 25., 32.7, and 31.7 per cent. below the result of experiment. As the two latter were the principal experiments, it is concluded that, generally, calculation gives the resistance nearly one-third less than what is obtained by actual and careful practice *.

2. ON THE RESISTANCE OF LEAD TO PRESSURE, AND ON THE INFLUENCE OF A SMALL QUANTITY OF OXIDE UPON ITS HARDNESS.

The recent experiments of Mr. Bevan on the compression of lead †, and his proposal of applying balls of that metal to estimate the force of presses, screws, &c., must be well known to English readers.

* Annales de Chimie, xliii. p. 224.

+ Quarterly Journal of Science, N.S., vol. vi., p. 392.

A similar investigation has been entered into by M. Coriolis, which, however, is much more refined as regards those circumstances that enable the lead to resist the force applied.

The points at first under investigation by the latter philosopher were temperature, time, impact, and state of the surfaces between which the lead was confined. The pieces of lead were cylinders 24 millimetres in diameter, and 19 in height; weighing each from 100 to 101 grammes. The arbitrary scale of measurement used gave 680 divisions for the 19 millimetres of height. The lead was pressed between two plates of iron in a kind of box, allowing lateral enlargement as the pressure was exerted, and the measurements of thickness were taken by means rendering the estimation very delicate.

To remove any irregularity resulting from differences in the times of pressure, it was in all ordinary cases limited to an exact minute. To ascertain the effect of impact, two pieces, which had been pressed equally, were then re-pressed, the one for two minutes, the other also for two minutes, but at eight different operations. On making thus the effect of impact eight times as much in one case as in the other, still the whole difference was only 19 divisions, which, divided amongst the extra 7 impacts, gives only about 3 divisions for each. As to the original temperature, its effect amounts to little or nothing; for when the cylinders were purposely cooled down, the mere effect of compression evolved so much heat that they could scarcely be touched, and this heat soon overpowered the original difference experimentally no sensible difference was produced. In reference to the influence exerted by the state of the surfaces between which the lead was pressed, this also proved to be insensible.

In the experiments the results are always expressed by the number of divisions to which the thickness of the lead has been reduced from the original standard thickness of 680 parts; and in this abstract we shall only give the mean results. Under the following pressures the ordinary lead used in mints was reduced to the expressed thickness.

When this lead was re-fused and cast, it was found to have increased so much in hardness, as with 1500 kilogrammes to give 490 degrees.

Lead was then reduced from the carbonate, and tried after being fused and cast once, twice, thrice, &c., care being taken as much as possible to prevent oxidation by the use of tallow, charcoal, &c., upon the surface. By the pressure of 1950 kilogrammes it was, after the first fusion, reduced to 333 degrees; after the second to 351; after the third, to 398, always setting off from the standard thickness of 680.

This effect was referred to a small quantity of oxide introduced

into the lead at each time of pouring. To ascertain the truth of this opinion, a stopcock was attached to the bottom of the melting vessel so that the lead could be drawn off without any contact with the atmosphere, the surface above being covered all the time with a thick layer of charcoal powder. Then the former experiments being repeated, it was found that lead, after the first fusion, was reduced to 303, less than on any former occasion; after a second, to 311; and, after a third, to 301; so that now no repetition of fusion produced any effect. Some of the lead was also cast in this way, being first raised to a cherry-red heat, and others only to the lowest point necessary for liquefaction. The effects were the same in both: no influence had been exerted over the hardness of the metal, and the changes which usually occur are due to a little oxide introduced, In experiments upon the influence of time it was found that, after a minute had elapsed, the effect of time was masked by the general effect of the metal, and nearly hidden. For a charge of 1950 kilogrammes the compressions were as follows:

So that here, after a minute, 10" produced an effect of only 2 degrees upon the scale. Still it was found the effect did proceed; for with a charge of 1760 kilogrammes the effect was as follows:

So that, after 24 hours, the lead still continued to give way.

The most important conclusion from these experiments is, that lead fused and cast in the open air is of variable hardness, and that to obtain it with its true and constant power of resistance, it must be cast out of contact of air, and drawn off from the bottom of the mass *.

3. ON THE POWER OF HORSES.-( B. Bevan, Esq.)

The following experimental data are from a letter written by Mr. Bevan to the Editors of the Philosophical Magazine.

"In the period from 1803 to 1809 I had the opportunity of ascertaining correctly the mean force exerted by good horses in drawing a plough; having had the superintendence of the experiments on that head at the various ploughing matches both at Woburn and Ashridge, under the patronage of the Duke of Bedford and the Earl of Bridgewater. I find among my memoranda the result of eight ploughing matches, at which there were seldom fewer than seven teams as competitors for the various prizes.

* Annales de Chimie, xliv. p. 103.