some length, the method of mine-surveying practised in New Spain, and the simple instruments employed for that purpose; and he takes occasion to recommend the adoption of the method then practised in Europe, which he illustrates by descriptions of the instruments, figures, and diagrams. (Vol. i. p. 327, &c.) The latter method being, in principle, though not in all its details, the same which is now pursued in the Cornish mines, it is unnecessary to refer to it more particularly.

The various machinery employed in mining and the reduction of the ores, is also described and illustrated by faithful, though rude figures. (Vol. ii. p. 189, &c.)

In another part of his work, the author discusses the expediency of opening the quicksilver mines of New Spain, and the probability of their admitting of being worked with advantage. The trade in quicksilver being monopolized by the crown of Spain, no mines of that metal were allowed to be worked, but those of El Almaden in Old Spain, and Guancavelica in Peru, and hence no progress was ever made in turning to advantage the quicksilver veins of New Spain. But that there are such veins, and that they might be worked to much advantage, is evident from the following passages:

In stating above, that we have not met with any account of mines of quicksilver having been worked in the early times after the discovery of the kingdom of New Spain, we are to be understood as referring to the sixteenth century, the era of the conquest; but subsequent to that period, many instances may be found.

First, some quicksilver mines were discovered in the jurisdiction of Chilapa, at sixty leagues distance from Mexico, to the southward*. Don Gonzalo Suarez de San Martin went over in August, 1676, to explore these mines, with a master smith and master bricklayer, and having set up a shed, a house, a smithy and furnaces, he had a part of the crest of the vein blasted away on the 14th of October, and commenced the works of San Mateo, San Joseph and Santa Catalina, all contiguous. He began three adits at a greater depth; but the hardness of the ground obliged him to remove half a league farther down, where, finding fair indications of success, he drove the work of la Concepcion. Here also he found very good ore, in a matrix of white spar, and drove a work, which he called los Reyes. He then drove an adit in a cross direction, and, at the distance of 47 varas, cut a vein of considerable size. Several assays were made of the ores from these works, both in the large and small way. Those from San Mateo yielded, by the minute assay, 12 ounces of quicksilver per quintal, those from Concepcion 25 ounces, those from the cross-cut 26 ounces.

* Villa Señor, Theatro Americano, tom. i., page 178.

'The second instance was during the viceroyalty of the Duke de la Conquista, who, in the year 1740, commissioned Don Philip Cayetano de Medina, an alderman of Mexico, and proprietor of the estate in which the Cerros of el Carro and el Picacho were situated, and Don Gregorio de Olloqui, an inhabitant of San Luis Potosi, to inspect some quicksilver mines in the aforesaid Cerros, which, according to Don Mathias de la Mota*, are in the jurisdiction of the Sierra de Pinos, in the kingdom of New Galicia. The result of this commission has not become known.

The third instance is that stated above, as having occurred in respect to these very mines of el Carro and el Picacho, in the year 1745, when the working of a newly-discovered mine of quicksilver was taken up by Don Fermin de Echevers, the president of Guadalaxara. On this occasion, we know from very good authority, that the vein was found to be rich, abundant, and easily worked, and equal to the supply of the whole kingdom of New Spain; and also, that upon the result of the reduction of some of the ore, conducted under the president's orders, the cost of the quicksilver amounted to no more than 22 or 23 dollars per quintal.

The fourth instance we shall mention, occurred previously to the last, being in the year 1743, early in the viceroyalty of Count Fuenclara, by whose order doctor Pedro Malo da Villavicencio, senior judge of the royal audiency, set out for the purpose of exploring some other quicksilver mines near Temascaltepec, the ores of which had been subjected to several experiments and assays at Mexico, by Don Manuel de Villegas Puente, factor of the royal stores, who now accompanied the senior judge; but their investigations failed of any beneficial result, and it appears that nothing but urgent necessity will ever induce the government to sanction the laws permitting mines of quicksilver to be worked, like those of silver, gold, or any other metal.

'Yet, as it is evident that there are within this kingdom mines of quicksilver, which the crown might at any moment order to be worked, nothing is easier than to demonstrate the expediency of adopting the same plan here, which has succeeded so well in the famous mines of Guancavelica in Peru †. For, first, whenever the supply of quicksilver fails, as has happened times without number, either in consequence of war, of losses at sea, or of the delay attendant upon procuring it from such a distance, the reduction of the ore in the amalgamation works is brought to a stand, the revenue is thrown into arrear, the whole kingdom suffers, the working of the mines is interfered with, and trade receives a check. By setting the quicksilver mines at work, all or most of these evils would be remedied, facilities would be afforded for reducing the silver in an expeditious manner, and the amount of the tenths, the one per cent. and the coinage duty would be augmented.'

Mota, MS. History of New Galicia, c. 62, n. fin.

+ Solorz. Polit. lib. 6, cap. 2.

In confirmation of the above, it may be added, that other veins of quicksilver, appearing, by the analysis of Professor Del Rio, to afford ores worth working, have recently been discovered in Mexico. Analyses of two specimens of the ore may be seen in the Philosophical Magazine for August, 1828.

The pits (shafts) and adits, by the aid of which the water is carried off from the mines, are then described.

These, with a chapter describing the operations of the mint of Mexico (vol. ii. p. 233), a vocabulary of mining terms (vol. ii. p. 320), and an enumeration of the mining districts of New Spain (vol. ii. p. 332), are the principal matters falling under the second head, which are treated by the author at length, and with these we shall conclude the present analysis; passing over the legal department of the subject, which, although forming the bulk of the work, might, we apprehend, be less interesting to the readers of this Journal.

Anatomische Untersuchungen über den Bau der Augen bei den Insekten und Crustaceen vom Dr. J. Müller zu Bonn. Mekel's Archiv für Anatomie und Physiologie. 1829.(Anatomical Investigations of the Structure of the Eyes in Insects and Crustacea, by Dr. J. Müller, &c. &c.)

6

THE original observations of Dr. Müller, contained in his Beiträge zur vergleichenden Physiologie des Gesichtsinnes, Leipzig, 1826," of which the present paper is a continuation, and which have subsequently been confirmed by G. Treviranus, Huschke, and Straus Durckheim, have hitherto been unnoticed in this country. They are of interest, however, not only as furnishing more correct ideas of the structure and character of the eyes of Insects and Crustacea than those generally received, but also as serving to remove the apparent anomalies by which they were supposed to be separated from the corresponding organs in vertebral animals.

It may not be superfluous to state, that, according to the usually admitted opinions, the structure of these organs, whether simple, conglomerate, or compound, is essentially similar; consisting in pyramidal prolongations of the optic nerve, covered by a uniform stratum of black pigment, and externally by a transparent cornea; the existence of a crystalline or vitreous humour being expressly denied. Such an organization, whilst it presents no analogy with that of the higher animals, places

insuperable difficulties in the way of all attempts of explaining the nature of the function, and naturally enough has been quoted in support of the extravagant doctrine which refers the seat of vision in the eyes of animals to the choroid.

The observations of Dr. Müller refer to the four different forms of eyes as they occur in Insects and Crustacea, viz. :— 1. Simple Eyes. 2. Aggregates of Simple Eyes. 3. Compound Eyes with facets on the external surface. 4. Compound Eyes without facets.

1. Simple Eyes.-The eye of Scorpions and Solpugæ have all the parts of the eyes of higher animals, viz., a retina surrounded by a layer of black pigment, a lens and vitreous humour, and lastly a cornea, convex externally. The black pigment, surrounding the cup-shaped retina, forms at the anterior edge of the vitreous humour a projecting belt, closely embracing the greatest posterior convexity of the lens. In Scolopendra morsitans there are four such simple eyes on each side of the head, of which three are circular, and the fourth and largest, elliptical. In all there is a hard, amber-coloured, and almost circular lens, in immediate contact with the posterior surface of the cornea. Each lens is lodged in a cupshaped retina, coated externally by black pigment. In these, as in most other simple eyes, there is either not any vitreous humour, or it is so small as to escape notice. In other cases, on the contrary, as Mantis religiosa, Gryllus hierogliphicus, and the larva of Dytiscus marginalis, there is reason to suppose it

exists.

2. Aggregates of Simple Eyes.-Of this kind are the eyes of Oniscus, Julus, Lepisma, Cymothoa, &c. In a large species. of Cymothoa, where the number of eyes thus aggregated was about forty, Dr. Müller found as many crystalline globes or lenses, one in contact with the posterior surface of each cornea; they were hard, transparent, and amber-coloured. Behind each lens was a larger globular mass, also transparent and amber-coloured, with a pit on its anterior surface, in which was lodged the posterior convexity of the lens. This larger mass was coated externally and posteriorly by a layer of black pigment, and in contact at its back part with a fibre from the common optic nerve, which probably is expanded into a cupshaped retina, situated between it and the stratum of pigment.

3. Compound Eyes with polygonal facets.-In many Crustacea, the existence of crystalline cones or prisms between the facets of the cornea and the fibrils of the optic nerve has long been known. Such were described in Astacus fluviatilis, by

Leuwenhoek and Cavolini; in Pagurus Bernhardus, by Swammerdam; in Limulus Polyphemus, by André.

In Penæus sulcatus, Dr. Müller describes the cornea as subdivided into quadrangular facets, and in contact posteriorly with a stratum of short crystalline masses, the lateral surfaces of which are coated by a greenish opaque pigment, separating them from each other. The crystalline columns, or prisms, are quadrangular, perfectly transparent, very short, being about as long again as they are wide, and in contact posteriorly with the fibrils of the optic nerve.

In Lucanus cervus (Coleoptera), the cornea is exceedingly thick, its facets being elongated like prisms. The crystalline bodies are conical, the bases being almost in contact with the cornea, whilst the apices are in contact with the extremities of the fibrils of the optic nerve, each of which is coated externally by a violet pigment.

A similar structure with some minor variations is also to be found in Orthoptera, Hemiptera, Lepidoptera, Hymenoptera, Diptera, and Neuroptera. As the general result of such observations, Dr. Müller describes the structure of such compound eyes as follows:-Behind the facets of the cornea is situated a stratum of elongated transparent prisms, in close apposition to each other, cylindrical or conical, and allowing the transmission of light in the direction of their longitudinal axis only, their lateral surfaces being coated with pigment. The proportion between their longitudinal and transverse diameters varies from 10: 1, to 2: 1. The anterior extremity, in contact with the cornea, is sometimes smooth, sometimes rounded. The pigment is sometimes black, as in Dytiscus, Blatta, Phalænæ, &c.; at others, as in Penæus, Locusta, Gryllus, &c. yellowishwhite, greenish, &c. though still opaque.

In some few cases the transparent cones are wanting, though their place is even here supplied by a thin transparent membrane, subdivided like the cornea into facets; e. g. in Vespa. crabro, Papilio rhamni, Libellula quadrimaculata, schna grandis. In Meloe maialis, the cornea is studded posteriorly with transparent projections, very convex, and almost parabolical.

4. Compound Eyes without facets.-In Monoculus apus the cornea, which is continuous with the common integuments, is smooth, and without facets; on removing it, the surface of the eye presents a dense aggregate of very small semicircular elevations, which terminate posteriorly in pointed cones, embedded in black pigment, and connected with the tuft