172 H. A. Newton— Fireball of January 13th, 1893. 



plate was 18°-8. The place where it entered upon the plate 

 was 72° 7 from the horizon measured *in the photographed 

 plane. These data show that at the entrance of the fireball 

 upon the photograph plate it was 17*6 miles from the camera, 

 and at the other margin of the plate it was 1575 miles dis- 

 tant. The length of the photographed track was five and 

 three-fourths miles. The altitudes above the earth were 16*5 

 and 12*5 miles respectively. According to the usual hypothe- 

 sis of the density of the air as we ascend, the barometric pres- 

 sure at the middle of the photographed track was a little less 

 than two inches, and the pressure was more than twice as 

 much at the low T er as at the upper point. The uncertainty in 

 the numbers in this article is not very great. The principal 

 cause of uncertainty is the want of exactness in the location 

 of the quit, and the triangles are so located that this cause 

 cannot largely affect numbers given. The residuals not ex- 

 ceeding 15" in (26) that indicate possible curvature correspond 

 to deviations of the path from a plane not exceeding 6 feet. 



39. In Plate III is given an enlarged print of the photo- 

 graphed track in six portions. It is about twenty six inches 

 long, so that it represents in length the track on a scale of 

 1 : 14000. The breadth of the track in the photograph at the two 

 ends is due to want of exact focus. Owing to changes dur- 

 ing the processes of reproduction the print shows the path 

 near its end much narrower than did the original plate. On 

 Mr. Lewis's plate the path shows near the end a clearly marked 

 central line and a smoothly limited marginal region five or six 

 minutes in breadth. The latter is only faintly reproduced in 

 the plate. 



40. The stone was evidently single during its passage across 

 the field of view. The breaking up which was noticed by 

 several observers took place lower down. 



The irregularities of light in the path increase notably in 

 frequency towards the end of the plate. At first they recur 

 only after hundreds of feet, while near the end they are per- 

 haps ten times as frequent. Such irregularities might be due 

 to small fragments breaking off from the main mass. But it 

 would seem reasonable that in that case we should be able to 

 detect small spurs of light from the path and of these I see no 

 trace. It seems much more reasonable to suppose that the 

 stony mass was in rotation, more rapid at the end than at the 

 beginning, and that unequal amounts of burned material were 

 thrown off according as a well burned or a raw surface was for 

 the instant in front. 



