,907.] PERTAINING TO WORK WITH A PORTRAIT LENS. 429 



III. Meteors. 



Slide 10. — This shows two large meteors which followed nearly 

 the same path across the plate. 



Slide II. — This shows the full flight of a large meteor on 

 1898, June 7. 



Slide 12. — These two pictures are of the same meteor, but with 

 two cameras 400 feet apart. The small scale picture was made by 

 Mr. Frank Sullivan with 3.4-inch portrait lens attached to the 40- 

 inch telescope during Professor Frost's spectroscopic observations. 

 The other was made with the 6-inch lens of the Bruce photographic 

 doublet. An inspection of the trail with respect to stars near which 

 the meteor passed shows a decided parallax. The distance of the 

 meteor above the earth's surface, from these two pictures, was about 

 90 miles. 



IV. Comets. 



Slide ij. — Swift's comet on 1892, April 7, showing a large 

 mass and separate system of tails which were going out from the 

 comet. 



Slide 14. — Giacobini's comet, 1905, December 29. The picture 

 shows the remarkable appearance of the tail, which on this date was 

 quite unlike the tail of any other comet. 



Slide 15. — Borrelly's comet on 1903, July 24. The second pho- 

 tograph on this slide was made by Mr. R. J. Wallace. The interval 

 between the two pictures is 3 hours. The tail which was separated 

 from the comet, had receded noticeably in three hours. Measures 

 of the plates showed that the particles forming the tail were moving 

 away from the comet at the rate of 29 miles a second. (See Astro- 

 physical Journal, October, 1903.) 



V. Vacant Regions and Holes in the Heavens. 



Slide 16. — This is a remarkable region of vacancies in a great 

 nebulous background in the constellation of Taurus. (See Astro- 

 physical Journal for 1907, April.) 



Slide 18. — Vacant lanes running from the nebulous region of 

 Rho Ophiuchi towards the east. 



Slide ig. — Great vacant regions about the star Theta Ophiuchi, 

 (See Popular Astronomy, No. 140.) 



Yerkes Observatory, 1907. 



