In a paper communicated to this Society in March, 1903, it was shown that antimonite is fairly transparent to radiations of long wave-length and that its behaviour between crossed nicols is consistent with orthorhombic symmetry. At the same time it was pointed out that it would be of interest to determine the wave-lengths of the radiations transmitted and the principal indices of refraction of antimonlte for these radiations. On undertaking this investigation it was soon found that antimonite was quite sufficiently transparent to the rays at the extreme red end of the visible spectrum to enable visual observations to, be made, and in a verbal communication to the Society on March 22, 1904, it was stated that the indices of refraction for red light were 4.129 for rays vibrating parallel to the axis Z and 3.873 for rays vibrating parallel to the axis X.

Lengenbachite is one of the interesting minerals which occur in the dolomite of the Binnenthal, and we owe our knowledge of it, as of many other new species, to the careful investigations conducted in recent years by Mr. R. H. Solly at that remarkable locality. The crystallographic and physical characters, so far as they have proved capable of determination, have been already described by Mr. Solly in the pages of this Magazine (vol. xiv, p. 78). The material which he kindly placed in my hands for chemical examination consisted of cleavage-plates, exhibiting brilliant metallic lustre, and of foliated aggregates of thin greyish-black crystals. Some of the crystals were partially covered with a thin, white incrustation readily removed by boiling dilute hydrochloric acid, a reagent which appeared to be without action on the lengenbachite.

The formula 2PbS. Sb2S3, given for jamesonite in all the textbooks, does not belong to jamesonite at all, but to the ‘Federerz’ (‘feather-ore’) from Wolfsherg in the Harz analysed by H. Rose in 1829, and for which the mineralogical names wolfsberglte (Huot, 1841) and plumosite (Haidinger, 1845) have been proposed. Rose's formula for the cleavable jamesonite from Cornwall was 3PbS. 2Sb2S3. In 1860 Rammelsberg united these, together with heteromorphite, under the name jamesonite and with the formula 2PbS. Sb2S3 a : this has since been followed in the textbooks, but, as will be pointed out below, it is very probable that there are here three distinct mineral species.

Before the value of hydrochloric acid forcblorine manufacture was recognized by soda-crystal makers, it was a common practice to get rid of the unpleasant fumes in the cheapest and most convenient way possible. At Messrs. Chance's works at Oldbury, near Birmingham, this was done by turning the gases from the salt-cake furnaces into a culvert which ran through some portion of the works. The better to condense the fumes, it seems probable that a brook, which runs near the works, was diverted into the culvert, thus forming a rough condenser. Some thirty years or so sgo, when alterations were being made at these works, a culvert of this description was unearthed and found to be lined with crystals of gypsum, which had formed on the brickwork. An old well, which was opened, was also studded with beautiful tufts of crystals. I am indebted to Mr. A. M. Chance for a handsome specimen with numerous attached crystals of gypsum, and also for some stereoscopic slides showing the well with the crystals in situ.

The mineral sartorite (of Dana) or scleroclase (of v. Waltershausen) appears to have been found much more frequently in latter years in the well-known dolomite at the Lengenbach, in the Binnenthal, Switzerland, than was formerly the case, and it may now be considered to be one of the commonest of the group of sulpharsenites of lead which have made this locality famous. Large, detached, longitudinally striated, prismatic crystals, mostly devoid of terminal faces, have been especially frequent, the majority of which are doubtless sartorites.

Professor Becke's paper on skiodroms marks an important advance in our knowledge of the shadows, or isogyres, which are seen when sections of crystals are examined in convergent polarized light. The isogyres can also be advantageously studied in mineral grains, where the irregular shape disturbs the distribution of the interference colours, but has much less effect on the shadows due to the coincidence of directions of vibration in the crystal with those of one of the nicols.

Previous work on the regular growth of crystals of salts on those of Minerals belonging to the same isostructural series led the author to the discovery that parallel deposition is conditioned by closeness, not of angle nor of axial ratios, but of molecular volume. Now although the substances previously examined resemble each other crystallographically, yet they exhibit such great differences in chemical properties, that reasonable doubt might be entertained whether conclusions drawn from them can be directly applied to isomorphous substances ; and it therefore became advisable to extend the observations to a group of the latter.

During the summer of this year certain crystals of zirkelite from Ceylon were entrusted to the author for crystallographical investigation, and in that connexion the specimens placed under this species in the British Museum collection were examined for the sake of comparison. The whole of the latter specimens come from Jaeupiranga in São Paulo, Brazil: some of them had been presented by Dr. E. Hussak and formed part of the material on which he and Dr. G. T. Prior conducted their investigation which led to the first discovery of zirkelite, while the remainder were purchased subsequently. The latter included a lot of small, brilliant crystals (numbered 86034 in the General Register) which differed so markedly in lustre from the other crystals as to suggest that they had been incorrectly determined.

Considerable confusion exists with regard to the nomenclature of the thirty-two possible classes of symmetry and their classification into systems. Each class is usually denoted by a name and a symbol ; but as every author invents his own names and symbols (the latter being often merely arbitrary numbers) the whole nomenclature is hopelessly confused. This is due to the fact that a different classification into systems, and consequently a different nomenclature is suggested according as the subject is approached (1) from the geometrical aspect based on the law of rational indices alone, (2) from the aspect of the structure-theory, (3) from the aspect of the practical crystallographer. Thus, for example, Dr. A. Schoenflies finds two distinct classifications necessary according as the subject is approached from aspect (1) or (2).