In the investigations usually given of the equilibrium of the stone bridge, it is assumed that the strains follow the same law as in the suspension bridge, the one being a case of stable, the other a case of instable, equilibrium; and, resulting from this hypothesis, formulæ are given whereby to determine the extrados suitable to a prescribed intrados.

This was an account of a series of experiments made in the Natural Philosophy Laboratory of the University, to test the applicability of Angström's method of periodic variations of temperature to the determination of low conductivity. The wood was cut into discs of a standard thickness, and these were very tightly secured together, after the interposition of copper-iron thermo-electric junctions (of very fine wire). One series of discs was cut parallel, the other perpendicular, to the fibre. The results were obtained very easily, and accorded satisfactorily with those obtained by more laborious methods.

To determine the cause of the ordinary zig-zag form of electric sparks, the author requested Mr Matheson, one of his laboratory students well skilled in photographic processes, to take instantaneous photographs of the sparks of the Holtz Machine, by means of a quartz lens, in hot and cold air alternately. Several of these photographs were exhibited, and showed much greater smoothness of the track of the spark in heated than in cold air. The zig-zag appearance seems to depend upon the presence of combustible organic particles in ordinary air, but the experiments are still in process.

The well marked “crag and tail” formation of North Berwick Law has long been appealed to by geologists as a striking example of the effects of those mysterious glacial currents, which at some time have wrought such changes on the surface of the globe. The Law presents, as is well known, a comparatively bold face, or crag to the west, against which the glacial current is supposed to have impinged, while, against its eastern face, there is a gently sloping mass of gravel, clay, and stones supposed to have been thrown up by this current under “lee” of the Law, and now forming what is called the “tail.” It had often occurred to me as remarkable, that so great a mass of debris should have been left by the passing current, whatever that may have been, on the eastern extremity of the hill, while it had apparently left no impression on the north and south sides, along which it must have passed.

A slight modification of a formula given by Sir W. Thomson (Phil. Mag. ii. 1871), shows that the period (t) of oscillation of a particle in a deep mass of liquid agitated by simple waves or ripples is

where λ is the wave-length, T the surface-tension, and ρ the density of the liquid. By producing, with the aid of a massive tuning-fork, steady ripples in various liquids all subjected to the same conditions, and measuring micrometrically the length of these ripples, the quantity T is determined with considerable accuracy from the above formula.

The only difficulty in this investigation is the selection of two liquids, neither of which will line the interior of the capillary tube so as to disturb the behaviour of the other. This was effected in various ways, most simply by employing water and sulphuric ether; for when these liquids are shaken together and allowed to come to rest, the result is the production of a very sharply defined bounding surface between a weak solution of water in ether (above) and a weak solution of ether in water (below). The observations and measurements were made with contiguous portions of the same capillary tube,–one dipping into the upper, the other into the lower, layer.

This note details various experiments made for me by Messrs C. M. Smith and A. Macfarlane in the Physical Laboratory of the University, and has been drawn up by these gentlemen. The only part I have taken in the work has been the suggestion of the line of investigation and the forms of apparatus employed. I mention this not alone injustice to them; but also as giving independent corroboration of results formerly arrived at by myself.

A considerable amount of time is lost in making an accurate weighing on account of the slowness of oscillation of the balance when the loads are nearly equal; and this loss of time is nearly proportional to the delicacy or sensitiveness of the balance. Hence it becomes a matter of importance to endeavour to bring the balance speedily to rest without, if possible, impairing its sensitiveness; as thus much time and labour would be saved in weighing. Several methods of applying gaseous friction for this purpose have been tried by me of late.

In the course of engineering works, bridges have to be thrown obliquely over rivers or over roads, and thus the construction of oblique or skewed arches is forced upon us. The skewed stone arch has not grown in favour, partly from the greater skill required in delineating and executing the forms, partly from the fact that such skewed arches have given signs of weakness. Hence an impression has gained ground that there is something defective in the principle.

In the first portion of this communication, the author discussed the general phenomena exhibited by the Palæozoic corals as regards their mode of growth and increase.

The Council having awarded the Makdougall Brisbane Prize for the Biennial Period, 1872–74, to Professor Lister, for his paper ‘On the Germ Theory of Putrefaction and other Fermentative Changes,” Dr Crum Brown, in requesting the Chairman to present the medal, addressed the Chairman as follows:—

Mr Chairman,—I have been requested by the Council, and I feel it a very great honour that I have been so requested, on the occasion of the presentation of the Makdougall Brisbane prize to Professor Lister, to state shortly the grounds upon which the Council have made the award.

When we direct the axes of the two eyes to any definite object, its different parts affect corresponding parts of each retina, and the object appears single. When we squint, or do not look direct at the object, its images affect non-corresponding parts of the two retinæ, and the object appears double. The more widely the axes of the eyes are deflected from the object, the further asunder the double objects seem; and the less the axes are deflected the less distant from each other the double objects appear. Thus, when we hold the finger in front of the eyes while we look at a distant candle or gas jet, the flame appears single and the finger double. When we turn the eyes to the finger it appears single and the flame appears double.

The difficulty experienced in determining the sulphur contained in the compounds of dimethyl-thetine (described in a former communication) by oxidation to sulphuric acid, induced the authors to study the effects of various oxidising agents on these compounds.

By acting on nitrate of dimethyl-thetine with dilute nitric acid, two bodies are produced. The one has acid properties, and forms a well-marked soluble salt with baryta. The other has neither acid nor basic properties. It crystallises in very beautiful needles from a hot solution in alcohol.