Page:The Scientific Monthly vol. 3.djvu/543

 WHAT WE KNOW ABOUT COMETS

��FiO. 10. Hallet'b Coubt, Jdnb fl and JtiNB T, 1910.

indicated in Fig. 11. The tail did not Beem to lag behind the position of the radius vector — the line passing through the sun and the comet's nucleus — because the observers on those days were nearly in the plane of the comet's orbit and the lag of the tail wm toward the observers. The velocity with which the structure moved out in the tail was strongly accelerated with the passing of time, as may be seen from the chart.

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