the cross-section forming the outer part of the diagram. A fuller description, with explanations of reasons for the various statements made, would extend beyond the limits suitable for this abstract. In the paper the author enters into some considerations as to the reasons for or against the views put forward by various persons. The paper concludes with a sketch of a contemplated experimental apparatus for illustrating the supposed motions in the earth's atmosphere by motions proposed to be brought into play in water placed in a horizontal circular tray, kept revolving round a vertical axis through its centre, and with heat applied round its circumference at bottom, and cold applied, or cooling allowed to proceed, in and around the central part at or near the surface. Transactions. Presents, March 10, 1892. Berlin :-Gesellschaft für Erdkunde. Verhandlungen. Bd. XIX. Königl. Preuss. Akademie der Wissenschaften. The Society. Sitzungs The Academy. Reports of the Cambridge, Mass.:-Harvard College. Annual 8vo. The University. Coimbra Coimbra :-Universidade. Annuario. 1891-92. The Society. Institute of Brewing. Transactions. Vol. V. London 1892. No. 3. 8vo. The Institute. Institution of Mechanical Engineers. Proceedings. 1891. No. 5. 8vo. London. Odontological Society of Great Britain. XXIV. No. 4. 8vo. London 1892. The Institution. Transactions. Vol. The Society. Journal and Trans actions. Vol. XVI. No. 5. 8vo. London 1892. The Society. Royal College of Physicians. List of Fellows. 8vo. London 1892. The College. Transactions (continued). Society of Antiquaries. Proceedings. Vol. XIII. No. 4. 8vo. Wien 1891; Denk 4to. Wien 1892; (Math.-naturw. Classe). Bd. LVIII. 4to. 8vo. Wien. The Academy. Observations and Reports. Cadiz :-Instituto y Observatorio de Marina de San Fernando. Almanaque Náutico para 1893. 8vo. Madrid 1891. Melbourne :-Mining Department. Reports the Quarter ended 30th September, 1891. The Observatory. and Statistics for 4to. Melbourne. The Department. Results of Me Stonyhurst:-Stonyhurst College Observatory. teorological and Magnetical Observations, 1891. 1892. 8vo. Clitheroe The College. Nivellement de Switzerland:-Commission Géodésique Fédérale. Précision de la Suisse. Vol. I. Livr. 9. Vol. II. Livr. 10. 4to. Genève 1891. The Commission. Trieste:-Osservatorio Marittimo. Rapporto Annuale. Vol. VI. 4to. Trieste 1892. The Observatory. Journals. Boletin de Minas, Industria y Construcciones. Año VII. No. 11. La Escuela Especial de Ingenieros, Lima. Nature Notes. Vol. III. No. 27. 8vo. London 1891. 4to. Lima 1891. The Editor. Records of the Australian Museum. Vol. I. No. 10. 8vo. Sydney 1891. Zeitschrift für Naturwissenschaften. 8vo. Leipzig 1891. The Museum. Band LXIV. Heft 4-5. Naturwiss. Verein für Sachsen und Thüringen, Halle. Bergbohm (J.) Neue Integrationsmethoden auf Grund der Potenzial-, Logarithmal-, und Numeralrechnung. 8vo. Stuttgart 1892. The Author. Blytt (A.) Nye Bidrag til Kundskaben om Karplanternes Udbre- Stokvis (B. J.) F. C. Donders. Amsterdam 1891. The Author. The Author. 1818-1889. [Obituary.] 8vo. Two plaster Medallion Portraits, of Dr. John Richardson, F.R S., and March 17, 1892. Sir GABRIEL STOKES, Bart., LL.D., Vice-President, in the Chair. A List of the Presents received was laid on the table, and thanks ordered for them. I. "Dynamo-Electric Machinery." By J. HOPKINSON, F.R.S., and E. WILSON. Received February 15, 1892. The following is intended as completion of a paper by Drs. J. and E. Hopkinson ('Phil. Trans.,' 1886, p. 331).* The motive is to verify by experiment theoretical results concerning the effect of the currents in the armature of dynamo machines on the amount and distribution of the magnetic field which were given in that paper, but which were left without verification. For the sake of completeness, part of the work is given over again. The two dynamos experimented upon were constructed by Messrs. Siemens Brothers and Co., and are identical, as far as it is possible to make them. They are mounted upon a common base plate, their axles being coupled together, and are referred to in this paper respectively as No. 1 and No. 2. Each dynamo has a single magnetic circuit consisting of two vertical limbs extended at their lower extremities to form the polepieces, and having their upper extremities connected by a yoke of rectangular section. Each limb, together with its pole-piece, is formed of a single forging of wrought iron. These forgings, as also that of the yoke, are built up of hammered scrap iron, and afterwards carefully annealed. Gun-metal castings bolted to the baseplate of the machine support the magnets. The magnetising coils on each limb consist of sixteen layers of copper wire 2 mm. diameter, making a total of 3968 convolutions for each machine. The pole-pieces are bored out to receive the armature, leaving a gap above and below subtending an angle of 68° at the centre of the shaft. The opposing surfaces of the gap are 14 cm. deep. * It must not be supposed from his name not appearing in this short paper that my brother, Dr. E. Hopkinson, had a minor part in the earlier paper. He not only did the most laborious part of the experimental work, but contributed his proper share to whatever there may be of merit in the theoretical part of the paper.-J. H. VOL. LI. E The following table gives the leading dimensions of the machine : The armature core is built up of soft-iron discs, No. 24 B.W.G., which are held between two end plates screwed on the shaft. The following table gives the leading dimensions of the armature : The core is wound longitudinally according to the Hefner von Alteneck principle with 208 bars made of copper strip, each 9 mm. deep by 1.8 mm. thick. The commutator is formed of fifty-two harddrawn copper segments insulated with mica, and the connexions to the armature so made, that the plane of commutation in the commutator is vertical when no current is passing through the armature. Each dynamo is intended for a normal output of 80 ampères 140 volts, at 880 revolutions per minute. The resistance of the armature measured between opposite bars of the commutator is 0.042 ohm, and of each magnet coil 13.3 ohms. In the machine, the armature core has a greater cross-section than the magnet cores, and consequently the magnetising force used therein may be neglected. The yoke has the same section as the magnet cores, and is therefore included therein, as is also the polepiece. The formula connecting the line integral of the magnetising force and the induction takes the short form n is the number of turns round magnet. c is the current round magnet in absolute measure. * Phil. Trans.,' p. 335. |
