On this point Mr Sorby explained in his address: 'On applying this method to the study of various minerals, the difference is found to be very great. We can mostly at once see whether they give a single unifocal image or one or two bifocal images, and form a very good opinion respecting the intensity of the double refraction, and easily determine whether it is positive or negative.... These facts combined furnish data so characteristic of the individual minerals, that it would usually be difficult to find two approximately similar.... It has been said that in studying the microscopical structure of rocks it is often difficult to distinguish nepheline from apatite. But the index of nepheline is about 1.53, whereas that of apatite is 1.64, and such a considerable difference could easily be recognised in a section not less than one-fiftieth of an inch in thickness.'
The observations hitherto made prove that minerals may be ranged in classes according to their refracting power and their chemical composition. The fluorides are lowest in the scale, while quartz, corundum, the sulphides and arsenides, are among the highest. From these particulars it will be understood that researches into mineralogy have a prospect of becoming more and more interesting.
As we have a British Association for the Advancement of Science, so our neighbours across the Channel have a French Association. It met last August at Havre, and in a few of its fifteen sections manifested signs of activity. Among the meteorologists, diagrams were exhibited shewing clearly that the 'changes of pressure in the upper regions of the atmosphere are by no means similar to those at the surface of the earth; for when the pressure at the lower station decreases, it rises at the upper station, and the reverse; or when it is steady at the one, it rises or falls at the other.' A line of telegraph for meteorological purposes is now erected from Bagnères to the Pic du Midi, seventeen miles. The Pic is nine thousand feet high, and will be an interesting observing station, in constant communication with the lower regions. A proposition was made that the Transatlantic steam-ship companies should be requested to institute regular meteorological observations on board their vessels; and that the captive balloon of next year's Great Exhibition at Paris should be an observing station. Paris is chosen as the meeting-place of the Association for next year, and at the same time a free international meteorological congress will be held.
During recent years it has been said that the marshes and saltish depressions in the territory of Algiers and other parts of North Africa were once covered by the sea, and schemes have been announced for readmitting the sea by cutting channels from the Mediterranean. Mr Le Chatelier, a French chemist, says—the existence of the salts is not due to the drying up of a former sea, but to the masses of rock-salt which exist in the mountains. From these the salt is dissolved out by rain or by subterranean waters, and the saline solution percolates the soil to feed the artesian reservoirs which underlie the desert. These observations will require attention from geographers.
If any apology were required for a somewhat late notice of Dr Sayre's method of rectifying curvature of the spine, it would be found in the fact that among the arts the healing art holds an eminent place, and has special claims on every one's attention. Dr Sayre, an American, has this year visited England to make known his method of curing those malformations of the backbone under which many persons remain cripples for the whole of their life; and now that it is known, the wonder is that it was not thought of before. In carrying out the operation, the patient is lifted from the ground, and suspended by a support under the chin and back of the head: sometimes a support is placed under the armpits, and sometimes the arms are raised. In this position the weight of the pelvis acts on the crook in the spine, and pulls it straight; a bandage dipped in plaster of Paris is then bound round the body; a few iron splints are inserted in the bandage, and as the plaster dries, a mould is formed, which keeps the straightened bones in place. The suspension is now at an end; the patient is found to be an inch or two inches taller than before the operation, and can walk without limping. After a few days, the plaster-mould is cut up each side, to allow of removal for washing the body; but the two halves are quickly replaced and held in position by a bandage. In some instances six months' wearing of the plaster-mould effects a cure, and the patient enjoys an ease and activity never before experienced.
This method of cure contrasts favourably with the treatment which keeps the patient supine many weary months. As may be imagined, it succeeds better with children than with adults; but even adults have been cured. A case occurred at Cork, the patient being a woman aged twenty-two, and requiring a little mechanical pulling to assist in the straightening; but it was accomplished, and she walked out of the room two inches taller than she entered it.
Mr Hoppe-Seyler, a learned German, has published a paper on Differences of Chemical Structure and of Digestion among Animals, supported by numerous examples, which shew that according to the organism so is the power to form differences of tissue; and he sums up thus: 'Looking at the question broadly, we find that the chemical composition of the tissues and the chemical functions of the organs present undoubted relations to the stages of development, which shew themselves in the zoological system, as well as in the early stages of development of each individual higher organism. These relations deserve further notice and investigation, and are qualified in many respects to prevent and correct errors in the classification of animals. It is generally supposed that the study of development is a purely morphological science, but it also presents a large field for chemical research.' This concluding sentence is significant, and should have serious consideration.
Waste pyrites from the manufacture of sulphuric acid is, as regards hardness, a good material for roads when mixed with gravel; but chemically it is not good. In the neighbourhood of Nienburg, Hanover, where roads and paths were covered with waste pyrites, it was found that grass and corn ceased to grow; and a farmer on mixing well-water with warm milk, observed that the milk curdled. The explanation is, that the waste pyrites 'contained not only sulphide of iron and earthy constituents, but also sulphide of zinc, and that by the influence of the oxygen of the atmosphere and the presence of water, these sulphides were gradually converted into the corresponding sulphates;' and these, continually extracted by the rain-water, soaked into the soil, contaminated the wells, and produced other injurious effects.
The want of really efficient names to distinguish various kinds of manufactured iron has long been felt in the iron trade. The Philadelphia Exhibition gave rise to a Commission which, after discussion of the question, have recommended that all malleable compounds of iron similar to the substance called wrought-iron shall be called 'weld-iron;' that compounds similar to the product hitherto known as puddled steel, shall be called 'weld-steel;' that compounds which cannot be appreciably hardened when placed in water while red-hot shall be called 'ingot-iron;' and that compounds of this latter which from any cause are capable of being tempered, shall be called 'ingot-steel.'
By further exercise of his inventive abilities, Major Moncrieff has produced a hydro-pneumatic spring gun-carriage perfectly adapted for use in the field. A gun mounted on this carriage could be made ready for action within ten minutes after its arrival in the trenches.