18G9.] ^'' ' [Mayer. 



length is loo 33', or 115,700 miles, and its greatest height is 75", or 33, GOO 

 miles. 



The protuberance No. 10, bears the most striking resemblance to a 

 caterpillar, out of whose head issue two horns; the one nearest the front 

 being the higher of the two, and terminated with a knob or ball from 

 which comes a broken line of light to the border of the moon. Its mean 

 position is 287° 33' and it extends through 11 degrees or 81,800 miles. 

 Its maximum elevation, which is at the head of " the caterpillar" is 

 52"; or 23,300 miles. 



"We here give a table of the position-angles and heights of the protuber- 

 ances. Those on the eastern limbs of the sun, viz: 1 to 7 inclusive, were 

 determined from measurements on the first plate of the totality series, 

 taken 17.1 seconds after second contact; those on the western limb of the 

 sun were determined from the last plate of totality, taken 50 seconds be- 

 fore third contact. 



The angles of jjosition of prominences, 1 to 7 inclusive, should be 

 diminished 32. '5, to make them correspond to the positions they had on 

 the first plate of totality; for reasons which are given in my official 

 report. 



Table of the position-angles arid heights of the Prominences. 



Ko. Prominence. Position-ansles. Ileisht. 



1 55° 9' to 57° 59' 22" 



2 6G° 14' to 72° 21' ........ 22" 



3 87° 15' 75" 



4 (base of)... 90° 25' to 98° 4' 82" 



4 (tip of N. wing) 90° 39' 



4 (tip of S. wing) 100° 10' 



5 101° 23' to 118° 30' 130" (nebulous cloud. ) 



146° 25' to 149° 3"' 45" 



7 156° 46' to 161° 59' 37" 



8 230° 13' to 245° 46' 75" 



9 ^ . . 273° 27' 



10 2S2o 13'to293ol2' 53" 



11 315° 54' to 331° 12' 44" 



12 342° 7' to 343° 58' 15" 



Observations on the application of photography to the determination of the 

 times of contacts dttring the transit of Venus in 1874 and 1883. 



"We here venture a few remarks, showing the peculiar value of photo- 

 graphy in the observations of the transits of Venus. 



It has been shown that the sun's image was photographed on the 

 camera plate with an exposure of only j-J-gth of a second; and the dura- 

 tion of exposure for any other instrument can be determined with as 

 great precision by the method which I employed. 



The instant the mechanical movement exposes the plate, it also records 

 the time of that exposure on a chronograph connected with a break-cir- 

 cuit clock, and thus we have an accurately delineated_/j5'w.?'6 of the transit 

 A. V. S. — VOL. XI — 2a 



