that from its upper part currents float away to both sides, northward and southward:--and that these currents continue in the upper regions of the atmosphere each of them advancing towards, and in part to, the high latitudes of its own hemisphere, until, by cooling, its substance becomes less buoyant, and sinks down gradually in various latitudes of that hemisphere, and forms itself into a return current towards the equator, in the lower part of the atmosphere. That the air of this great cap of atmosphere, covering the middle and higher latitudes, and including portions of the currents just described, having come from the equatorial regions, which were moving absolutely from west to east in the earth's diurnal rotation with a velocity of about 1000 miles per hour, must, on coming into those new regions much nearer to the earth's axis, have greater velocity from west to east than the earth below it in those new regions has. That in the central or polar part of this great revolving cap of air the barometric pressure must be abated in consequence of the centrifugal tendency due to the extra speed of this great whirling cap of atmosphere. That the bottom layers of this great cap of atmosphere, being by friction on the earth's surface retarded as to this extra velocity of rotation eastward, must have a diminished centrifugal tendency as compared with the quicker revolving air above them, and, consequently, tend to flow, and actually do flow, inwards, towards the region of abated barometric pressure at the centre of the revolving cap of air. That thus, over the middle, or middle and higher latitudes, there are three currents: (1.) A top main current towards the pole. (2.) A bottom subordinate current towards the pole. (3.) A middle main current in direction from the pole, and constituting the joint return current for both the preceding currents. And that all these three have a prevailing motion from west to east, in advance of the earth. That the great return current, flowing in direction from the pole towards the equator, arrives at a certain part of its course at which it ceases to revolve eastward in advance of the earth; and, for the rest of its course to the foot of the equatorial rising belt, it blows along the surface of the earth as the trade wind of the hemisphere in which it is situated. The description here given of the author's theory, it is to be noticed, is only a brief sketch. The aërial motions which have been described are illustrated by the accompanying diagram (Plate 1). The arrows on the surface of the hemisphere represent the winds at the surface of land or sea, not the currents in the higher regions. The northward and southward motions, and the up and down motions, in the main currents of the atmosphere, are indicated for all heights in 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. No. 3. 8vo. 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. Transactions (continued). Society of Antiquaries. Proceedings. Vol. XIII. No. 4. Wien 1891; Denk (Math.-naturw. Classe). Bd. LVIII. 4to. 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 Me8vo. Clitheroe The College. Nivellement de Stonyhurst:-Stonyhurst College Observatory. teorological and Magnetical Observations, 1891. 1892. Switzerland:-Commissiou 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. 4to. Lima 1891. La Escuela Especial de Ingenieros, Lima. Nature Notes. Vol. III. No. 27. 8vo. London 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. Karplanternes Udbre- Blytt (A.) Nye Bidrag til Kundskaben om 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 |