ed to in the constructing of public buildings, in which lectures, sermons, or other discourses, were intended to be delivered. He drew the attention of the Section to two distinct cases, first, where, as in a church, the speaker is, for the most part, placed in one fixed place; second, where, as in the Houses of Lords and of Commons, the speakers require to be heard from many various quarters. The author then gave some remarkable instances of the great distances at which sounds had been heard ; one of the most curious of which instances was, that when the fleet engaged, we believe, in the blockade of Copenhagen, were in a very extended line, ships at the one end distinctly heard, and recorded in their logs, a loud cannonade, which they heard on a particular day; and it was found afterwards, by a comparison of the logs of the ships, that this very cannonade proceeded from the proving of large pieces of ordnance, which had been conducted for the greater part of a day at a dockyard in the neighbourhood of one end of the fleet, from which the other end, at which the reports were heard, was distant three hundred miles. He also mentioned several well authenticated cases, where the human voice had been heard distinctly at a distance of between one and two miles, and stated, that in numerous experiments made in the open air, under every variety of circumstances, in the neighbourhood of Edinburgh, in which he was assisted by a number of different individuals, they found no difficulty, when the atmosphere was still, of carrying on a conversation at distances varying from 200 to 1000 feet. Dr Reid concluded, accordingly, that where there is any difficulty in the communication of sound in large buildings, this must arise generally, not so much from any want of power in the voice of the speaker, as from a prolonged reverberation maintained between the walls, or between the floor and the roof, and wherever this was observed, there would be no deficiency of sound, or rather noise, but a great want of all purity of tone or distinctness of articulation. He then shewed how the reverberating of sound from the ceiling, walls, and floor of a room, by being continued too long, and interfering with each other, would have the effect of producing a confusing noise, and thus interfering with the hearing of the succeeding parts of the discourse. From all the premises which he had previously laid down, he concluded, that

low roofs, having a good reflecting power, rough and interrupted walls, and a floor either possessing very little resilience, such as earthen floors do, or, if boarded, then much broken and interrupted by irregular seating and matting, produced a building best suited to the hearing of a speaker in many directions. He exhibited a plan of his own chemical laboratory in Edinburgh, in which these particulars were all exemplified; and he declared that a speaker, expressing himself in a tone very little above a whisper, could be heard in the most remote parts of that room, whether crowded or empty. The space not occupied by furnace arrangements can accommodate about a thousand persons. The power of the voice being proportioned to the intensity of the sonorous impulse, the area through which it has to diffuse itself, and the manner in which it is strengthened by reflection, all superfluous space ought to be avoided as much as possible, and the direct sound of the voice having been strengthened by one reflection from the roof, it ought then to be entirely absorbed, by being made to fall upon some non-reflecting surface. Dr Reid then alluded to several public buildings in Dublin, where practical illustrations of the views he had explained might be obtained; and, after a number of observations upon the form, walls, roof, ornamenting, &c. of public buildings, and the manner in which many might be much improved, alluded to the influence of different strata of air in the same apartment, arising from imperfect ventilation, or from an equal distribution of heat, which he shewed had considerable effect in some peculiar situations in preventing the free and equal communication of sound.

10. Mr Snow Harris on the nature of electrical attraction, with cxperiments. The author is of opinion, that neither the theory of one nor of two fluids explains all the phenomena of electrical attraction and repulsion. He makes exceptions to the law of the inverse square of the distance, as much depends upon the state and circumstances of the bodies as evinced by delicate experiments. He exhibited his apparatus for measuring the force of attraction between electrified plates and spheres. Some observations made by Professor Powell and Mr Whewell shewed that plates will attract nearly as the inverse distance of the molecules attract in the inverse square. Mr S. Harris explained, and remarked, that it was not his object to refute the theory of

Melloni, or the law of the inverse square of the distance, but that his views were perfectly consistent with facts, and enabled him beforehand to estimate the degree of the attractive focus acting on substances of all shapes, at all distances, by conduced and induced electric action. Professor Stevelly made some remarks to reconcile theory with experiment.

11. Mr J. S. Russel gave a short account of his experimental researches into the laws of the motions of floating bodies. He detailed experiments on two canals in Scotland. He shewed that small models are not applicable for exhibiting the resistance of large vessels, the distinction between the conditions of a floating and an immersed body, with the differences from any theory, and that resistance diminished with great velocities. He exhi bited a table of results, and deduced from it that the difference in different canals, according to size and depth, is dependent on the velocity of the wave raised. A member stated that the results are confirmed on two canals in Ireland, but gave a somewhat different explanation. Another member confirmed the results.

Wednesday, 12th August.-12. Mr Pritchard exhibited some experiments on polarization this morning before the meeting; they consisted chiefly of improvements in the mode of exhibition. The most singular fact shewn was, the formation of a certain white elliptic ring, by light passing through calcareous spar.

13. Mr Snow Harris, on the use of the proof, plain, and torsion balance of Coulomb and others. He detected considerable differences in the distribution of electricity in different parts of bodies, and obtained results apparently at variance with Poisson's theory. He compared various theories, and exhibited experiments in support of his views. Mr Whewell made some remarks on the experiments of Mr Harris, and on the utility of theories to assign causes. He differed from Mr Harris as to the inferences from the experiments, and shewed, that many of the supposed exceptions are really quite accordant with the mathematical theory.

14. Captain Sabine gave an account of Hansteen's researches on terrestrial magnetism, who had collected observations on the

variation of the needle in different parts of the globe, and demonstrated that there are two magnetic poles in each hemisphere. He exhibited maps of the variation at different dates, and shewed that the line of no dip was not a great circle, but inflected. He noticed the excursion of Hansteen to determine the magnetic poles and variation in Siberia, the observations of Captain Ross and others; and concluded by remarking the absence of any data for determining the position of the southern pole.

15. Professor Wheatstone examined with a prism the line of light formed by the voltaic spark between charcoal points. The spectrum was complete without interruption, but marked by certain lines of more intense brightness. With the electric light from a surface of mercury, a few very bright lines of definite colour appeared separated by wide dark intervals. The same light from different metallic surfaces gave similarly interrupted spectra; the divisions being distributed in a peculiar manner in the spectra for each metal. In alloys and compounds of different metals, the lines peculiar to each wire were compounded. The voltaic light from a surface of mercury, and of other metals in succession, gave analogous results. At different points of the connecting wire the light appeared of different colour; that colour was found marked with a peculiarly bright line in the corresponding spectrum. High characteristics afford the means of distinguishing the different metals, and to determine the origin of the electric light in different cases. The light from combustion of metals gave uninterrupted spectra ; thus shewing, that voltaic light is not related to combustion. The light of the electric spark from contact of different metals gives similar light and dark spaces to those in the voltaic. Mr Wheatstone applies these results to the theories of electric light, and thinks they point out the volatilization of ponderable matter from the conductors, as the most probable hypothesis.

16. The Rev. Mr M'Gauley exhibited and explained a new principle, consisting in the application of magnetism as a moving power. The apparatus consists of two powerful electromagnets, so arranged that the contact is alternately changed from one pole to the other, and the poles of the magnet thus reversed. This produces an alternate motion in the bar connect

ing the poles, which moving a crank turns a wheel and any machinery connected with it. The inventor has succeeded in thus getting a moving power nearly equivalent to the lifting power of the magnet. The main peculiarities may be thus stated :— 1st, The reversing apparatus easily applied, without almost sensibly altering its weight, to any number of electro-magnets. 2d, The connexion of the reversing apparatus with the vibrating bar. 3d, The direct application of the entire, or nearly the entire, lifting power to machinery. 4th, The action of several electro-magnets, without their interfering with each other.

17. Mr R. W. Fox on a new Dipping Needle. The instrument which shews, at once, the dip, intensity, and variation, was exhibited. It contains graduated circles, moving in altitude and azimuth, and a vertical index adjusted to the meridian, turning in azimuth till the needle is vertical. Hence the dip may be deduced, and the intensity, by comparing the effect of a small magnet, introduced.

Professors Stevelly and Lloyd made some remarks. The accuracy of the instrument was confirmed by the testimony of Sir John Franklin, who had examined it in connexion with Messrs Christie and Barlow, even under extreme conditions.

18. Professor Hamilton on the theory of Logologues, and other numbers of higher orders. He discussed the nature of algebra, and whether it is to be considered a science, or only a language? His leading idea is, that it may be regarded as the science of pure and abstract time, as geometry is the science of pure space; and that the distinction of positive and negative corresponds to past and future. He regards imaginary quantities as couples of moments, or couples of steps: a given moment as having a given position, in regard to time, as a given point in space each step has direction and magnitude. He referred to his paper in the Irish Transactions, which contained his suggestions for certain improvements and simplifications in algebra.

Thursday, 13th August.-19. Mr R. Roberts exhibited an apparatus by which figures may be seen, or sentences read, as distinctly when revolving at a high velocity, as when in a state of quiescence. It illustrates, also, the duration of light on the

eye.