Reference Number. [To face page 28. .) Birmingham; (H.) Hawkhurst, Kent; (L.) Regent's Park, I... 25 195 +64 Draconis...... G. L. Schultz. R. P. Greg. 3... 4... 53? 26 63? 50 +54 a Persei.. 73? 23 +58 Cassiopeia +62 € Cassiopeia T. Wright, W. Marriott, W. Barber. A. S. Herschel, T. Wright, W. Marriott. A. S. Herschel. W. Barber. A. S. Herschel. T. Wright, W. Marriott, W. Barber. T. Wright, W. Marriott, W. Barber. W. Barber. A. S. Herschel. Average velocity and position of the radiant-point of the Perseids, Nos. 11, 12, 13. meteors thus identified, together with the particulars of the observations from which they are concluded, are entered in the Table opposite. The accompanying diagram (drawn on the same scale as that in the last Report) readily exhibits to the eye the actual heights at appearance and disappearance (or the heights of the centres of the visible paths of the meteors Nos. 1, 4, 9) above the earth's surface. The last vertical line on the right represents (as in the last Report) the average height at first appearance and that at disappearance of all the meteors regarded as identified in the present list, of which the approximate heights of those points have been satisfactorily ascertained. The resulting average heights are: Heights at appearance and disappearance of thirteen shooting-stars simultaneously observed at the Royal Observatory, Greenwich, and at other stations in England, August 6th-11th, 1870. (Nos. 1, 4, 9 are calculated heights at the centres of the real paths.) The present average heights are somewhat less than those observed in the year 1863; but they agree more closely with the general average height at first appearance, 70.05 miles, and that at disappearance, 54-22 miles (as given in the Report for 1863, footnote on p. 328), of nearly all the shooting-stars [To face page 28. .) Birmingham; (H.) Hawkhurst, Kent; (L.) Regent's Park, 1870. city Position of the radiant-point. es r Observers, Remarks, &c. ad. 1... 25 195 3... 4... 53? 26 63? 50 +54 simultaneously observed until the beginning of that year. The average velocity of the Perseïds, relatively to the earth, observed in the year 1863 was 34.4 miles per second, and that of the three Perseids satisfactorily well observed in the present list is 37 miles per second. In his original letters to Father Secchi on their connexion with Tuttle's comet (Comet III., 1862), now universally accepted as a true basis of their cosmical theory, Prof. Schiaparelli calculated, from the known elements of the comet's orbit, that the velocity with which the Perseïds enter the earth's atmosphere (allowing for a very minute influence of the earth's attraction) is 38 miles per second. That the direct determination of the velocities of the August shooting-stars which were made last year should, in this instance, so exactly agree with the value found by calculation (although from the small number of identifiable meteors the probable error of the determination is rather large), is, from the great scale and general excellence of the observations, at least provisionally, a successful confirmation of the astronomical theory of the August meteors, and a satisfactory conclusion from the simultaneous watch. 2. During the corresponding observations of the meteor-shower of November last, in which the observers of Mr. Glaisher's staff at the Royal Observatory, Greenwich, also took an important share, the coincidence of the times of appearance and of the other particulars of a single meteor only of the shower simultaneously observed at Greenwich and at Tooting, near London, could be established, the descriptions of which, as given by the observers at those stations, were as follows:: 15 1 5 56 Greenwich... Length of path 15°. Observer, WM. MARRIOTT. 15 1 5 0 Tooting Meteor fairly well observed. Observer, H. W. JACKSON. The apparent paths of the meteor among the constellations present a considerable parallax in the right direction of displacement, as seen from the two observers' stations, to lead to a positive determination of its real altitude above the earth. The concluded path of the meteor is nearly horizontal at a height of about fifteen miles above the earth's surface. The small distance (only seven miles) between the two stations, greatly increasing the effect of the errors most difficult to avoid in the observation and description of such transitory phenomena, must, however, for the present be regarded as precluding certainty from the conclusion, which would otherwise attach to this unusually low elevation of a meteor's real path. |