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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



fOcT. 



tion of Swansea, Ihe principal inhabitant?, magistracy, and (lie country 

 gcDllemen of (he neighboiirliood, and by tlie memljers of the Royal Insti- 

 tution of South Wales, to attend the meeting at Southampton for the pur- 

 pose of inviting the British Association to hold their annual meeting at 

 Swansea at as early a period as may suit their convenience. The (ieneral 

 Committee will therefore have before them at this meeting invitations from 

 Oxford, Norwich, and Swansea. 

 Southampton, Sept. 9, I84G. 



Proceedings of Sections. 

 SiiCTio.s A. — Mathematical and Physical Scienci;. 

 President: Sir J. F. VV. \\tric\\t\.— Vice-Presidents: Sir D. Brewster, 

 Prof. AVheatslone, Col. Colby, Dr. M hewcll.— ,S>iTW«r(es; Dr. Stevelly, 

 Messrs. G. G. Stokes, J. Drew. — Committee: Prof. Oersted, M. Svan- 

 berg. Prof. M'ortmann, Messrs. .Vlkn, W. R. Birt, Hon. and Rev. C. 

 Harris, Messrs. W . S. Harris, R. Aunt, Dr. Lee, ^\\■. J. Phillips, Rev. 

 Dr. Robinson, j\lr. F. Ronaldo, Capt. Sir J. C. Ross, R.N. Mr. .1. Scolt 

 Russell, Col. Sabine, Rev. Dr. Scoresby, Rev. Dr. M ilson. Rev. R. 

 Walker, Mr. J. A. Dale, Dr. Green, Col. Everest, Mr. R. W . Fo.x, 

 Prof. Eicenlohr, 



Sir J. I". M. Heijschel, President, on taking the chair, explained the 

 objects of the Association. 



The first paper read was a Report, " On Gauss's Magnetic Constants," 

 from I'rofessor Erman. — The author, aftor pointing out, by several ex- 

 amples, the uselessness of accumulating, beyond certain bounds, mere 

 observations, without subjecting them to scientific reduction, and llie im- 

 portance now attached on all hands to such reductions — as exempliljed in 

 the case of the reduction of all the Greenwich Observations, lately executed 

 by the Admiralty, at the solicitation of the British .Association — a work 

 ■which M. Ressel welcomed in the last moments of his life as the beginning 

 of a new period in astronomy ; and, after instancing the fact ihat the Asso- 

 ciation had been compelled to discontinue many valuable and systematized 

 courses of meteorological (ibservations, in consequence of the stores of un- 

 reduced observations outstripping their power to have them reduced, 

 stated, that the determination of the Gaussian magnetic constants had ap- 

 peared to them at the meeting at Cambridge last year, of such importance, 

 that a sum of 59/. was entrusted to him, for the purpose of reducing certain 

 observations made by him on terrestrial magnetism during the year 1S29, 

 at several stations round the earth ; and applying them to the purpose of 

 determining those constants for that year. The present report was a state- 

 ment of the results already obtained from this arrangement. The obser- 

 ■vations to be reduced had been made by M. Erman, from the year 182S to 

 1830, at 650 nearly equidistant stations, along a line encircling the globe 

 between the latitudes 02° N. and 60°S.:— at each station the dip, the 

 horizontal direction, and the intensity had been observed. The labour of 

 reducing these had not only far exceeded Ihat which he (M. Erman) could 

 afford to bestow on it, but even the leisure of an industrious and intelligent 

 young mathematical friend, M. Petersen, to prosecute the task ; and the 

 report now detailed the extent to which he had gone in his labours. 



" On the Bands formed hij the Partial Interception of the Prismatic 

 Spectrum." By Professor Pow ell. 



" On the C'liistitution a':d Forces of the Molecules of Matter." By Dr. 

 l,AMi>G.— This was an elaborate theory of the molecular constitution of 

 matter ; applied in forty-two distinct propositions lo the explanation of 

 gravitation, temperature, and specific lieats of gases, cohesion, allinilies, 

 Jatent heat, volume, disturbances of electrical eipiililirium, and other 

 electrical phenomena, with electro motion and cleclro-chemical deconi- 

 posiiion. One remarkable consequence of this theory is, that gravitation 

 depends on the electrical atoms ahme; and tliat hence a positively elec- 

 trified body must be heavier, and a negativdv eleclritieil body, lighter than 

 the same body with its electricity in the onliiiarilv undisturbed state. This 

 the author projiosed to prove experimentally to the Section by an expe- 

 riment to which he was conducted by the th'eorj-, as soon as he could pro- 

 cure a cylinder electrical machine with an insulated rubber. The pre- 

 sident proposed that discussion on the communication should be suspended 

 until Mr. Laming had exhibited this experiment. 



" Reiwrt on Recent researches in Hydrodi/namirs." By G. B. Stokes. 

 —This report was divided into the following heads:— 1. General theories 

 connected with the ordinary equations of fluid motion. 2. Theory of 

 waves, including tides. 3. The discharge of gases through small orifices. 

 4. Theory of sound. 5. Simultaneous oscillations of fluids and solids. 

 6. Formation of the equations of motion, when the pressure is not sup- 

 posed equal in all directions. The first head referred to investigations of 

 a rather abstract nature. L'uder the second, the researches of Mr. Green, 

 Professor Kelland and Mr. Airy, on the subject of waves, were particu- 

 larly alluded to, and the accurate agreement of theory with the experi- 

 ments of Mr. Scott Russell pointed out. The important investigations of 

 Mr. Airy on the the theory of the tides, were also mentioned. Under the 

 next head were mentioned some experiments of MM. Barr^ de Saint- 

 Tenant and Wantzel, by which an empirical formula was obtained for the 

 velocity of discharge of air through a small orifice, when the discharge is 

 produced by a considerable dillerencc of pressure. The common formula 

 does not apply to extreme cases. A memoir, by Mr. Ureea, on the reflec- 

 tion and n fraction of sound was then alluded to — a memoir which is re- 

 markable from its bearing on the physical theory of light. The investiga- 

 tioDs mentioned under the fifth head related principally to the motion of 



pendulums in resisting media. Mr. Green has solved the problem in Ihe 

 case of an o.-icillaMng ellipsoid. The last head contained a notice of the 

 theories of i\lM. Navier, Poisson, and others on the irregularity of pres- 

 sure in dilTereut directions about the same point. This theory may be con- 

 sidered to be that of the internal friction of fluids. 



Dr. WiiEWELL thought he had ample reason to congratulate himself and 

 the Section on the success of the advice which he had given when, in the 

 year 1830, his friends Mr. Harcouit and the Dean of Ely, had consulted 

 regarding the proper objects which such an association as the then con- 

 templated British Association should propose to itsidf. He had then 

 advised that one very prominent object should he the preparation of 

 reports on the actual state of human knowledge in the several deparlnients 

 of science. — and one of the frnits of that advice had been the very able 

 report which had just been presented by his friend Mr. Stokes. Mhen he 

 contracted the present scientific position of British philosophers with what 

 it had been only sixteen years ago, when Britain was vastly behind the 

 continental philosophers, not ouly in scientific attainments, but even in the 

 knowledge of what had been achieved by others, he could not but congra- 

 tulate all concerned that that stigma bad been so completely wiped away. 

 Dr. Whewell then proceeded to comment on several parts of the report 

 and pointed out the importance of keeping distinctly before the mind the 

 essential dilference between two kinds of waves, in one of which the mo- 

 tions of the particles of the fluid were the same from the top to the bottom, 

 in the other, the mulions of the particles, while all circular, or rather 

 elliptical, diminished rapidly until at the bottom it became nothing. Of 

 this latter kind a familiar illustration could be had by watching the waves 

 which the wind produced as it swept over fields of standing corn or long 

 grass. He then adveited to the formation of the double wave — an example 

 of which was afforded by the tides at Southampton; and which had been 

 investigated by Mr. Scott Russell in the Forth, and by others at Ipswich. 

 He then briefly reviewed the theoretical researches of Weber, iiellaud, 

 and Airy, on the subject of waves; and concluded by sajing, that as 

 waves of sound were reflected eciioes, so he conceived they must suffer 

 refraction, though the observing of this was attended with experimental 

 difticulties ; but that these waves were diflracled, he conceived no one 

 could doubt who would attend to the varying sound of a cascade as you 

 approached it round a bending course, it being at first hidden from sight 

 by interposed rocks, banks, or other obstacles. The President agreed 

 with Dr. Whewell, and not only did he conceive that sound could be re- 

 flected, refracted and diflracled, but pointed out several cases, as in some 

 of the phenomena of the tuning fork, where something closely analogous, 

 at all events, to polarization must take place. 



" Notice of a New Property of Light exhibited in the Action of Chrij- 

 sammatc of Potash upon Common and Polarized Light." By Sir D. 

 Brewster. — The chrysammate of potash, which chiystallizes in very 

 small, flat rhombic plates, has the metallic lustre of gold, whence it derives 

 its name of golden fluid. M'hen the sun's light is transmitted through the 

 rhombic plates it has a reddish yellow colour, and is wholly polarized ia 

 one plane. AVhen the crystals are pressed with the blade of a knife on a 

 piece of glass, they can be spread out like an amalgam. The light trans- 

 mitted through the thinnest films thus produced, consists of two oppositely 

 polarized pencils —the one of a bright carmine red and the other of a pale 

 yellow colour. AVith thicker films, the two pencils approach to two 

 equally bright carmine red pencils. It is to the reflected light, however, 

 and its new properties, that 1 wish to direct the attention of the Seciion. 

 Common light, retiecled at a perpendicular incidence from the surfaces of 

 the crystals, or of the films, has the colour of virgin gold. It grows less 

 and less yellow as the incidence increases, till it becomes of a pale bluish 

 white colour at very great incidences. The compound pencil, thus re- 

 flected and coloured, consists of two oppositely polarized pencils — one 

 polarized in the plane of refleciiou, and of a pale bluish white colour at all 

 incidences, ami the olhtr polarized perpendicular to the plane of refleition, 

 and of a golden yellow colour at small incidences, passing successively 

 into a deeper yellow, greenish yellow, green, greenish blue, blue, and light 

 pink, as the angle of incidence increases. This very remarkable property, 

 which I have discovered also in some olher crystals, is not caused by any 

 film of oxide formed upon the natural surface of the crystal, nor is it the 

 result of any change produced upon the surface by external causes. It is 

 exhibited, under the usual moditications, if the surface of the chrysammate 

 is in optical contact with fluids and with glass : and when the crystal is in 

 the act of being dissolved, or when a fresh surface is exposed hy mecha- 

 nical means, the superficial action uf the cryslal upon light is in both cases 

 the same. When the chrysammate is re-ciystaliized from an aqueous 

 solution, it appears in tufis of prisms of a bright red colour, the gulden 

 rellection being overpowered by the transmitted light; but when these 

 tnfts are spread into a film by pressure, the golden yellow colour re-appears. 

 When the crystals of chrysammate are healed \\ ith a spirit lamp, or above 

 a gas burner, the}' e.rplode with a flame and smoke like gunpowder; aud, 

 by continuing the tieat, the residue melts and a cross of colourless amor- 

 phous crjstals is left, i have found the same explosive properly in the 

 aloetinate of potash. 



Dr. Whewell conceived this was raiher a curious action of the chry- 

 sammate aud aleotinate of potash on light than any new property of light. 

 7he President, Sir .1. HEnscHi L, was inclined to agiee in that opinion, 

 since nothing was more clearly established than that the colours ultimately 

 exploded by light reflected i'rom the surfaces of bodies depended on the 

 number of superficial particles which (he light penetrated in the first in- 



