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Early in the year 1912 extensive modifications were introduced in the apparatus for slitting rocks, and for grinding and polishing thin-sections in the Mineral Department of the British Museum, the whole of the alterations and additions being carried out to my designs by Messrs. Plume and Parry, 47 Old Compton Street, London, W. The changes made were chiefly in the means for holding the specimen or section during the operations; much of the actual machinery remained unaltered, and some of it dates back to the initial installation, upwards of forty years ago. It may not, therefore, be without interest if a brief description of the history of the installation be included with the description of the present apparatus.

The mineral schwartzembergito was first described by Domeyko in 1864 as an oxychloroiodide of lead from the Desert of Atacama. The specimens, which are said to have been collected about ten leagues from Paposo in the Desert of Atacama, at a mine worked for argentiferous galena, were brought to his notice by Dr. Schwartzemberg, an assayer at Copiapo, who had recognized the material as being an iodide of lead. Domeyko made a chemical analysis (see p. 82) of the mineral, a yellowish crust, 1 to 2 mm. in thickness, upon galena, and obtained the formula, 2Pb(CI,I)2.3PbO, the specific gravity being 5.7; no crystal measurements were obtainable, neither were any optical observations made.

During recent years a systematic survey of the mineral resources of Ceylon has been in progress, in connexion with which a large number of specimens have been sent to the Imperial Institute for examination. In 1905 several cases containing coarse gravel from the streams of the gem-district of Balangoda were received. The constituent minerals were mainly zircon, tourmaline, corundum, spinel, ilmenite, together with small quantities of geikielite, fergusonite, and other rare-earth minerals. Last summer during the examination of these gravels one of the authors found three black crystals witll unusually brilliant faces. The apparently monoclinie form and the general physical characters at once suggested the crystallized native zirconia, baddeleyite, and this conjecture was confirmed by the goniometrical measurements and the chemical analysis.

Early in the year 1918 Mr. Atehur Russell picked up at the old antimony-lead mine at Glendilming in Eskdale, Dumfriesshire, Ipecimens of the antimony-lead ore Jound there, in which were small cavities lined with a drusy layer of mimlte crystals; these, being markedly deeper in eolour than the stibnite forming part of some of the specimens, belonged to a different species, and probably a sulphantimonite of lead. Mr. Russell blought some of the specimens to the Museum, and some of the small crystals were examined with the view of determining the species to which they belong.

In this paper are embodied the results of an examination of the specimens of lead slags from Laurium in the British Museum. On some of the specimens a new mineral, paralaurionite, was found, which possesses the same chemical composition as laurionite, but entirely different morphological and optical characters.In addition to crystals of the four minerals given in the title, a few crystals oi matloekite and anglesite were noticed, and on one specimen there is a radiating group of prismatic crystals of penfieldite.

The object of goniometrical measurement is to determine in the simplest and quickest manner possible the geometrical constants of crystals and the indices of their faces. The ideal instrument should enable the observations to he conveniently and quickly made, and present them in such a form that the indices of the faces may be easily calculated. It is claimed for the tbrm of goniometer described in this paper that it does approximate to such an instrument. Before entering into the description it will not be out of place to discuss briefly the two types at present in existence, and point out their advantages and disadvantages.

Of the various methods employed or suggested for the graphical representation on a plane of points on the surface of a sphere, the most important to the crystallographer are the stereographic and the gnomonic projections. Both are in common use, and both have their particular advantages. Professor Penfield has recently published a series of papers in which he points cut the advantages that accrue from the employment of the stereographic projection both in crystallography and cartography. He has devised protractors and scales, which facilitate the construction of the projection of the poles of the faces bounding a crystal or of portions of the earth's surface, and enable the angles between points or contained by zones, i.e. great circles, to be readily determined from measurements on the plane diagram.

Analyses of Indian manganese-ores generally show the presence of small amounts of arsenic. The form in which this constituent occurs was discovered by Dr. L. Leigh Fermor in the course of his investigations of these well-known deposits. At two different localities crystalline arsenates were found. One of these occurrences is at the Sitapar deposit in the Chhindwara district, Central Provinces. The pinkish-white to white arsenate found there is the new mineral to which we have given the name fermorite. The other locality at which an arsenate was found is Kajlidongri, Jhabua State, Central India. The pale-green arsenate, somewhat resembling apatite in appearance, which occurs at this locality has been found by us to be identical with the tilasite from Sweden described by Sjögren.

The validity of Haüy's great law of the rationality of intercepts — better known as the law of rational indices—or its equivalent, the law of homogeneity of arrangement of the ultimate particles in a crystalline structure, has as yet never been seriously called into question : nevertheless, in the crystals of the telluride of gold, calaverite, we find characters which are to all appearance at variance with this law. As far as the author is aware and can ascertain, no difficulty of a precisely similar kind has ever been encountered before. Certain substances do, indeed, display the so-called optical anomalies; but these are, as was first established by Mallard, in reality in strict accordance with the actual crystalline arrangement.

To mineralogists probably few spots in the world surpass in interest the little quarry hollowed out of the dolomite, just where the latter is cut by the Lengenbaeh, and about half a kilometre above the point where this stream ends its hurried course by joining the Binna at Imfeld, a hamlet lying in the main valley three kilometres above the village of Binn.

Some interest attaches to crystals of krennerite, since this mineral has apparently the same composition as calaverite, the crystalline development of which presents such peculiar features. After completing the study of crystals of the latter substance, the author naturally turned his attention to krennerite to ascertain whether any similar peculiarities were noticeable, but nothing abnormal could be detected.Good crystals of krennerite are rare. The Mineral Collection of the British Museum has however a specimen from Nagyág, on which are dotted numerous small crystals possessing a large number of brilliant faces. This specimen was examined by Prof. H. A. Miers rather more than twelve years ago, and the measurements of one good crystal are recorded in this Magazine.

For many years past Mr. R. H. Solly has been accustomed to spend each succeeding summer in the quest of mineral specimens in the neighbourhood of the village of Binn, Switzerland, particularly of those occurring in the white crystalline dolomite of the Lengenbach quarry, and his patient energy has been rewarded by the discovery, not only of material which has thrown fresh light on previously known minerals, but also of specimens which on examination proved to represent species new to science. Especially important was the discovery in 1903 of small, and often minute, blood-red crystals which differed both in colour and in streak from realgar, a common mineral in the quarry.

About two years ago there was brought to the British Museum a specimen covered with numerous mall cubes—so the crystals appeared to be—of the bluish-green colour suggestive of a mineral containing copper. Judged by their form the crystals might be beleito, but a qualitative analysis by Dr. Prior, while revealing the presence of chlorine and copper, showed no trace of lead. A crystal was then removed from the specimen and measured on a goniometer, and the discovery was at once made that these apparent cubes are iu reality rhombo-hedra with an angle of nearly 88° between adjacent faces. Since no previously known oxychloride of copper crystallizes in this form, these crystals were evidently worthy of further investigation.

In this paper are recorded the observations made upon four exceptionally good specimens of atacamite in the British Museum, which have been submitted to careful study with tile object of determining the geometrical and physical characters of the mineral with greater accuracy than has hitherto been possible. The axial ratios have been calculated with the utmost refinement, an attempt has been made to determine the crystallographic symmetry by a study of the etched figures, and the values of the principal indices of refraction have for the first time been obtained.

A DETERMINATION of the refractive power, which need be accurate to the second place of decimals only, is of considerable service for the discrimination of transparent substances, such as, in particular, faceted gem-stones. If tbe substance be so highly refractive that a total-reflectometer be not available, the method of minimum deviation is the simplest that can be used. Although the well-known formula 9 A + D sin 2

Nearly ten years ago, in 1902, five small crystals were noticed by one of us on a crystal of a sulpharsenite of lead, probably rathite, which had been found in the Lengenbach quarry that summer. Although from their lead-grey colour they also appeared to belong to a sulpharsenite of lead, in habit and appearance they were unlike the crystals of any such species as yet known. The crystals were measured, and were shown at the anniversary meeting, of the Society, November 18, 1902, but the measurements were not published at the time in the expectation that further material would afterwards be found which would enable an analysis to be made and perhaps throw fresh light on the morphological characters of the crystals.

Among the specimens that were presented to the British Museum by Dr. C. T. Trechmann in 1917 from the collection of his father, the late C. O. Treehmann, was a loose crystal~ which at first sight appeared to belong to one of the lead-grey species so long associated with the Binn Valley, but measurements made on the three-circle goniometer in the British Museum did not accord with the angles recorded for any of the species hitherto described. The crystal was recently submitted to a careful examination, but still the bi-angular co-ordinates of the faces differ from those given for any other species, and the only conclusion that can be drawn is that the crystal represents a new mineral species, and one peculiar to the Binn Valley.

During recent years a considerable industry has grown up at Paris in the synthetical manufacture of corundum for jewellery purposes by means of the process devised by Professor A. Verneuil. In place of the fragments of natural ruby used in previous attempts, ammoniumalum is the material employed. After careful preparation to free it from potash and other impurities, it is ground to a powder and placed in a sieve at the top of the oxygen tube of an inverted blowpipe. The sieve is tapped by a hammer at regular intervals, and uniformity is in this simple way produced in the amount of powder that falls; the necessary adjustment is effected by varying the height through which the hammer falls. To minimize the cost of production, a few alterations have been made in the original apparatus.

When investigating the morphology of crystals, such as those of schwartzembergite, which are so rounded or striated as to afford no definite reflections of the object-slit of the goniometer, the author found most serviceable a camera lucida which could be attached to the eye-piece of the telescope of the goniometer, and thus used for the direct drawing upon paper of the ‘light-figures’ given by the crystals, the ordinary signal being replaced by a pin-hole. The cap of the eye-piece in use is unscrewed and the camera lucida is fixed to the tube by means of four clamping screws.

In a previous paper the author pointed out the advantages of a three circle form of goniometer in the determination of the morphological characters of crystals ; the crystal is adjusted once for all, and measurements may be made in any desired zone. A description was added of such an instrument, which had resulted from the addition of a two-circle apparatus to an ordinary Fuess goniometer with a single horizontal circle. This instrument has been in almost daily use since the end of June, 1899, and the author is, therefore, in a position to appreciate the ease and celerity with which crystals, however small, may be in this manner measured. As was remarked in the paper quoted above, the adapted instrument has the disadvantage that measurements can only be made through little more than a right angle from the pole in which the zone to be measured and the zone of reference intersect, and, therefore, only half a zone can be measured without readjustment of the circles B and C.

This form of goniometer was designed in order to provide for the use of students of elementary crystallography, at as moderate a cost as possible, an efficient instrument for the measurement of the interracial angles of crystals. It is of the customary type, in which the direction of reference is given by the reflection of a distant object in a small plane mirror without optical aid, and the axis of the grHduated circle is horizontal. The mirror measures about 45 by 25 ram. and its frame is rigidly attached to the ball of a ball and socket joint, so that it is adjustable in any direction; the socket is split, and a screw linking the halves enables it to grip the ball firmly.