« 
D. P. Todd—The Transit of Venus, 1882. 135 
bore. The chronograph was attended by Professor Welcker, 
late of the University of California, who made also the obser- 
vations with the thermometer and barometer. 
irteen reversals of the plumb-line were made during the 
period of the exposures. The exposing-slide was moved to the 
east and to the west, alternately with each exposure, this order 
never being varied for any reason whatever. I invariably 
moved the slide, and made all the necessary entries pertaining 
to each picture in the photographic record myself. 
perature of the photographic house, in which there was no fire, 
was frequently read from a standard thermometer, the range 
being from 65°-7 at 19" 51™, to 75°-4 at 23" 38™. This latter 
was the time of the last exposure preceding interior contact at 
egress. After I had observed this contact optically, ten addi- 
tional exposures were made. 
Of the Photographic Record proper there are three copies; the 
original was deposited in the vault of the Observatory, the 
duplicate is now in my possession at Amherst, and the triplicate 
was left in the safe of the Lick Trust Office, San Francisco. 
he total number of plates exposed was 147. Subtracting 
from this number all those exposed at the beginning of the 
day, the ten made between the two contacts at egress, a few 
worthless ones, and all others of doubtful value, the total num- 
ber of plates which are available for micrometric measurement 
cannot fall far short of 125, and may somewhat exceed that 
number. 
Before the plates were finally packed in the boxes I made a 
comparative estimate, based on a somewhat rapid examination, 
of the value of these photographs of the transit. Each plate 
was taken up in order, and a mark assigned to it, on the scale 
A, A—, B+, B, B—. The mark A means that the plate was 
Judged to be of the very first quality, and capable of the most 
accurate measurement. Those marked A— are a shade infe- 
rior. Second grade plates are designated by B, those a shade 
better, but not so good as A—, being marked B+; while 
those not quite up to the grade B are marked B—. A few 
were judged to be worth only a still lower mark, ©. The 
result was as follows: 
A 71 B 9 
Ase oon OB Bevis Total, 128 
Bae a8 C 4 
Mr. Lovell was ably assisted in the photographic work by 
Mr. Milton Loryea, of San José, whose services were very 
kindly rendered to the Observatory without compensation, and 
by Mr. A. P. Flaglor and Mr. O. vy. Lange, who were engaged 
from San Francisco. 
