portion of sulphur obtained from it by analysis being exactly the total quantity that should be contained in the three sulphurets of which this substance consists. The specific gravity of this substance, compared with those of its ingredients, also indicates that the combination is attended with an expansion nearly proportionate to the numbers 6000:5765.

2. The author, proposing to avail himself of the opportunity afforded him by this inquiry, to enter into an investigation concerning the various ores that are produced by the combination of sulphur and copper, of the nature of which neither mineralogy nor chemistry has yet supplied us with any certain information, thinks it necessary, in the second part of his paper, to offer some remarks concerning the different modes of attraction that appear to influence the formation of mineral substances.

Two kinds of attraction have hitherto been admitted to prevail in the formation of mineral substances, viz. the attraction of composition, and the attraction of aggregation. The former, which is more generally known by the name of chemical attraction, takes place only between the most simple or primitive molecules of a substance; which, however, must be of dissimilar nature: and to its action is owing the formation of new, or, as they may properly be called, secondary or integrant molecules; because they, and they only, determine the nature of all the compound bodies belonging to the mineral kingdom. The difference existing between mineral bodies is now said to depend-1st, Upon the nature of the primitive molecules, by the combination of which they are produced; and 2ndly, Upon the proportion in which these molecules, supposing them to be the same, are combined together. The combination of these secondary molecules is effected by the attraction of aggregation, which unites them into one or several masses, perfectly homogeneous in all their parts. This attraction of aggregation seems to be susceptible of various modifications, which alter its manner of acting upon the constituent molecules. Of these, two are here mentioned:-1. The crystalline attraction of aggregation; and 2. The simple attraction of aggregation. The former always takes place between similar molecules, and is either regular, irregular, or amorphous. The first of these produces solid bodies, which are either constantly of the same form, or subject to certain laws of variation, which are always capable of being referred to the same primitive form. This, like all other crystalline attractions, can only take place in fluids, which, among other conditions, must be at rest when it is operating. When the fluid happens to be agitated, the crystallization will then be of the second kind, and the forms produced will be irregular: and when the agitation of the fluid is still greater, small irregular detached masses will subside, and unite together by a mode of attraction, which is here called simple homogeneous attraction of aggregation, of which instances are given in the granulated quartz and granulated carbonate of lime. This attraction operates at times simultaneously with the simple homogeneous attraction; and then the granulated masses, instead of

being composed of an aggregate of irregular grains, will appear to consist of small crystals of a very regular form, as may be very frequently seen in manganesian carbonate of lime. At other times, again, the molecules, instead of uniting together by the influence of the crystalline attraction of aggregation, are precipitated in a detached but confused manner; and then a simple aggregation takes place, which banishes all appearances of crystallization, and affords the aspect which has been distinguished by the name of compact or earthy.

This last, or the amorphous species of crystallization, is here described as being that kind which, though it produces no determinate form, is nevertheless the result of a regular aggregation. This is thought to depend on the peculiar form of the primitive molecules; such as, for instance, the globular, or others approaching to it. Calcedony, girasol, and pure transparent steatite, appear to owe their origin to this mode of formation. And here the author enters into a minute disquisition concerning the cause of the deception which has often taken place, and has led several experienced mineralogists to ascribe to these substances, especially the chalcedony, a certain degree of regular crystallization.

Besides these attractions between similar molecules of substances, there exists another, between such similar molecules and others which are dissimilar, or of a different nature. This introduces what may be called an heterogeneous attraction of aggregation, which is much weaker and more variable than any of the others, and produces substances which can no longer be called chemical combinations. In these, the dissimilar ingredients may, and often do, vary in proportion, according to the different circumstances under which they are formed; as, for instance, in those kinds of tremolite which have the dolomite for matrix where the carbonate of lime is in the proportion of bb; whereas in those kinds which have an argillaceous matrix, it is only in the proportion of

Although these heterogeneous compounds be not attended with any changes in the chemical nature of their ingredients, yet they frequently, as has already been observed, admit of an alteration in their physical construction, and very often induce variations in such of their characters as more immediately depend upon that construction; such as, their specific gravity, their hardness, their transparency, and even (particularly in the class of stones) their colour. Hence it appears that the mineralogist cannot pay too much attention to this mode of attraction; since, by a due application of it, he will be enabled to understand the accidental causes of the variations to which those substances are liable. Nor should the chemist be less mindful of such an agent; since, by neglecting that precaution, he will be constantly exposed to confound those products which really belong to the chemical composition of the substances which he examines with those which are foreign to it.

At the close of this part of the paper, the author acknowledges that the different kinds of attraction here described may be nothing

more than simple modifications of one and the same power, originally belonging to matter; but he maintains, at the same time, that these modifications certainly exert as much force, at the time of their operation, as could be exerted by attractive forces that are really different.

In the third part, which treats of the different kinds of sulphuret of copper, we are first apprised of the importance of this inquiry, by the observation, that, on comparing the different characters of this substance with those of the triple sulphuret described in the first part of this paper, we shall find that the antimony and the lead, which have been generally considered as constituent parts of the last-mentioned ore, are, in fact, nothing more than accidental ingredients, introduced merely by the attraction of aggregation.

In the sequel of the paper, the author introduces an ample stock of observations and analyses respecting various cupro-sulphurets, which have been hitherto very imperfectly examined. And first he treats of the gray tetrahedral sulphuret of copper, which is found to consist of copper, iron, and sulphur, in different proportions; the gray copper ore, called Fahlerz by the Germans, being of the same composition. The yellow copper ore, or Kupferkies of the Germans, appears to be double sulphuret of copper and iron, but constituting a species distinct from the gray sulphuret of the same tetrahedral form. Among these, there is one in particular which has not yet been described as belonging to this ore; namely, the dodecahedron with rhombic planes, which has hitherto been found only in Cornwall, and there only in small quantities, though in crystals of considerable size. It is also shown at length wherein most of the characters of the tetrahedral yellow cupro-martial sulphuret differ from those of the octahedral sulphuret of iron.

The following question is next proposed, and strongly recommended to the future investigation of mineralogists. As the true sulphuret of copper and the fahlerz are of a blackish gray colour, how comes it that the kind of cupro-martial sulphuret, commonly called pyritical copper, has always that brilliant yellow colour which particularly characterizes it, and which is the principal cause that leads many mineralogists to consider it as being nothing more than a martial pyrites mixed with copper? The solution of this difficulty, we are told, will materially contribute to ascertain the external characters of this kind of sulphurets.

The cupro-martial sulphuret, called by Werner Buntkupfererz, is a new species of this ore, which crystallizes in forms that are peculiar to it, and not at all analogous to those of the other cupro-martial sulphuret. The ingredients, which are solely copper, iron, and sulphur, differ considerably in their proportions in different specimens.

The author desires that what he has here said may be considered merely as a cursory account of some of the sulphurets of copper, from which, however, he thinks it may be inferred, that there exists a great number of species of this substance which have not yet been de

scribed, and that many of those with which we are acquainted have not been sufficiently examined.

A general observation, which he tells us is founded upon long experience, is, that there exists a great variety of minerals which have the same substance, or collection of substances, for their basis, and are combined with the same modifying substance, but whose differences arise merely from the variety of proportions in these bases or substances.

The paper closes with an earnest exhortation to those who cultivate mineralogy, to choose for the subjects of their experiments a variety of perfect specimens from different districts, and as much as possible from different matrices; that they make a number of comparative analyses; and that the mineralogist and the chemist mutually sanction the operations of each other in their respective departments.

Analysis of a triple Sulphuret, of Lead, Antimony, and Copper, from Cornwall. By Charles Hatchett, Esq. F.R.S. Read January 26, 1804. [Phil. Trans. 1804, p. 63.]

This is the analysis to which the Count de Bournon more than once refers in his elaborate account of the same mineral, lately read to the Society. We find here, in addition to the information contained in that paper, that one of the reasons why this very scarce ore has been hitherto so little attended to, is probably its great resemblance to an ore of antimony; that by all the chemical tests by which it has been tried, its constituent parts are manifestly lead, antimony, copper, and a small proportion of iron, the whole combined with sulphur; and that when the specific gravity, the external and internal colour, the fracture, the grain, and other characters here described are considered, there can be no doubt that the three first metals exist in the ore in, or nearly in, the metallic state, combined with sulphur, so as to form a triple sulphuret. The proportion of the ingredients are as given by Count de Bournon, who, in fact, took them from this paper.

Observations on the Orifices found in certain poisonous Snakes, situated between the Nostril and the Eye. By Patrick Russell, M.D. F.R.S. With some Remarks on the Structure of those Orifices; and the Description of a Bay connected with the Eye, met with in the same Snakes. By Everard Home, Esq. F.R.S. Read February 2, 1804. [Phil. Trans. 1804, p. 70.]

The orifice, which is the principal object of this paper, has been long since noticed by naturalists, who conceived it to be the external organ of hearing. Dr. Russell, in the many opportunities he has had of observing a variety of snakes, has particularly examined them with respect to this feature; and he here informs us, that he has found in the whole class (exclusive of the rattle-snake,) fifteen or

sixteen species of Coluber, and three of the genus Boa, which have these lateral orifices; that they have not as yet been discovered in the genus Anguis; and that in general it appears that only venomous snakes have this distinctive character.

From Mr. Home's description and remarks, we learn that these orifices do not lead to the nostril or to the ear, but to a distinct bag of a rounded form, there being within the skull a hollow of the same shape, surrounded by bone, which seems purely intended to receive it. This cavity is described as resembling a cup, formed by the bones of the skull and those of the upper jaw, and not unlike the orbit. The bags bear a relative proportion to the size of the snake; they are, like the eyelids, lined with a cuticle, which forms the transparent cornea, making a part of the outer cuticle; both which, it seems, are shed at the same time.

Mr. Home proceeds next to a description of similar bags in the deer and antelope kinds, which were by some thought to be lachrymal glands or ducts. On close examination, however, it is found that these bags have a secretion of their own, and that there is no reason for thinking that tears ever pass into them, the passage into the nose being unusually free, and the orifices of the bags in general unfavourably situated for the reception of the tears. The use to which the fluid secreted in these bags is applied, is as yet unknown. In the snake this apparatus has that position which seems best adapted to pour out the fluid upon the cornea when the head of the snake is in an erect position.

An Enquiry concerning the Nature of Heat, and the Mode of its Communication. By Benjamin Count of Rumford, V.P.R.S. Foreign Associate of the National Institute of France, &c. Read February 2, 1804. [Phil. Trans. 1804, p. 77.]

The importance of the investigation here entered into,-inasmuch as it applies to most of the operations of nature as well as art,-appears so manifest, that we shall not recapitulate what the author advances on that subject. Before he proceeds to the detail of his experiments for the purpose of computing the emissions of heat from various bodies under a variety of circumstances, he finds it necessary to premise a minute description of the principal part of the apparatus he contrived for his purpose. This instrument consists of a hollow cylindrical vessel of brass, four inches long, and as many in diameter. It is closed at both ends; but has at one end a cylindrical neck about eight-tenths of an inch in diameter, by which it is occasionally filled with water of different temperatures, and through which also a thermometer, constructed for the purpose, is occasionally introduced, in order to ascertain the changes of temperature in the fluid. As it was in the first instance only meant to observe the quantity of heat that escapes through the sides of the vessel, two boxes were, contrived, filled and covered with non-conducting substances, such as eiderdown, fur, &c., which were fitted to the two ends or flat surfaces of