426 BARNARD— ASTRONOMICAL PHOTOGRAPHY [April 20, 



known. Such an instance occurred at the Yerkes Observatory 

 where the same meteor was photographed with two cameras (by 

 Mr. Frank SuUivan and the writer) separated by 400 feet only. The 

 parallax or displacement of the trail among the stars was clearly 

 shown. Measures of these two plates show that the meteor was 

 about 90 miles above the earth's surface. 



In Plates II and III are given specimens of meteor photographs 

 selected from a great number of such plates. The lower photo- 

 graph, of Plate II (region of M 11, exposure 2 hours 40 minutes), 

 shows the trails of two meteors which were nearly in a straight line, 

 so that, at first thought, one would suppose it was the trail of one 

 meteor which had been interrupted near the middle of its flight. 

 Both meteors were moving toward the south, it is assumed (for 

 they were not seen by the observer), and were undoubtedly Lyrids 

 — having a radiant in the constellation of Lyra. 



Plate III (a 17 hours 20 minutes, 8 south 15° ; exposure i hour 

 34 minutes) shows in the first case the full flight of a meteor which 

 evidently exploded near the end of its path, as indicated by that 

 portion of the train which is of greater brightness. The lower pho- 

 tograph shows a great meteor trail and Brooks comet, IV, 1893 

 (exposure 2 hours 5 minutes). The bright trail was caused by a 

 very large meteor which was seen by the observer. It was moving 

 toward the southeast and exploded just off the edge of the plate. By 

 one who is regularly photographing the sky with these rapid lenses, 

 meteors are thus frequently caught in their flight. 



Comets. 

 Plate V shows two views of Giacobini's comet (c 1905). The 

 first of these (December 29, exposure i hour 38 minutes) is the 

 most interesting because of the peculiar form of the tail of the 

 comet. The edges of the tail are convex and sharply defined, and 

 they taper to a narrow neck where they join the head, which is quite 

 large. The tail was doubtless a hollow cone. There is a narrow 

 hazy strip running from the lower or south edge of the tail near the 

 middle of the plate. In the original this can be traced across the 

 edge of the tail onto the tail itself. On the next night, December 



