132 D. P. Todd—The Transit of Venus, 1882. 
ished completely within two hours; and on three or four occa- 
sions clouds were observed very near the horizon, but they 
never rose. The wind blew in fitful gusts night and day the 
3d and 4th, and the morning of the 5th. But very soon after 
12 o'clock, that day, the winds entirely subsided, and for the 
next fifty or sixty hours the utmost tranquility prevailed, the 
temperature never falling below 60°, and rising to very near 
70° in the shade at noon on the day of the transit. 
Optical—The sun rose about 7 o’clock, December 6th, with 
Venus a good way on its disk. The planet was observed by 
Captain Floyd at intervals throughout the time of transit, with 
the twelve-inch equatoreal of the Observatory; and with this 
instrument he made several drawings, and observed the two con- 
tacts at egress. The photographie operations were suspended 
just before the two contacts; and I observed these with the 
four-inch transit instrument, mounted on its reversing carriage. 
Photographic.—The horizontal photoheliograph, with which 
the pictures of the transit of Venus were taken was constructed 
by Alvan Clark & Sons, and is, in all essential parts, entirely 
similar to those made by the same makers for the American 
Transit-of-Venus Commission. The general theory of this in- 
strument was first published by Professor Harkness in volume 
xliii of the Memoirs of the Royal Astronomical Society ; and 
subsequently by Professor Newcomb in the “American Obser- 
vations of the Transit of Venus,” 1874, Part I, where a detailed 
ciently large to insure their absolute stability in every part. 
The first pictures with the Lick photoheliograph were made 
with dry plates by Captain Floyd, November 19th, two days 
before I arrived on the mountain. These confidently assured 
me that the instrament, although not then in adjustment, and 
in some parts lacking, was capable of work of the best sort. 
A suitable exposing-slide had not been provided by the 
makers; this, however, arrived within two or three days, and 
