322 0. A. Young—Observations of the Transit of Venus. 
ment on the evenings of both Dec. 5th and Dec. 6th. e also 
received the Washington noon signals on the 5th and 6th; and 
after correcting them for the errors of the Washington clock 
(obligingly communicated to me by the Superintendent of the 
Naval Observatory), the accordance between the results of these 
signals and the star observations was complete within 0°03. 
t local mean noon on Dec. 5th, the clock was slow 14°88, and 
gaining 0*030 hourly. A mean-time clock, in the same room 
with the sidereal, was kept in continual comparison with it, 
both of the clocks recording their beats upon the same chrono- 
graph sheets all through the Transit. 
clock was determined by Mr. McNeill with the Transit instru- 
6 WwW 
rd 
Ill. Osservers anp INSTRUMENTS. 
1. Dr. S. Alexander, Professor Emeritus of Astronomy. 
This gentleman used a 3}-inch telescope by Fraunhofer, equa- 
torially mounted. The eye-piece was an erecting one with & 
power of about 80, and a thick, neutral-tint shade glass. Dr. 
Alexander took his time from a mean-time chronometer, which 
was compared with the observatory clock before and after the 
observations. 
2. Professor C. A. Young, in the Halsted Observatory. The 
instrument was the great 23-inch equatorial of 30 feet focus, 
with a polarizing helioscope, the first reflecting prism of whic 
is hollow and filled with water circulating through it. The 
magnifying powers used in the observation of the contacts was 
160. At the two internal contacts the aperture was reduced to 
58 inches, in order to make the observations comparable as far 
as possible with those of the various government expeditions. 
At the external contacts and during all the micrometric a0 
spectroscopic observations the full aperture was employed. 
8. Professor C. G. Rockwood, also in the Halsted Observ® 
tory. He used a dialytic telescope of 4 inches tag belong- 
ing to himself; it was equatorially mounted, and had the usual 
reflecting solar eye-piece with magnifying power of 113. 
4, C (son of Professor Young). His instrument 
was the finder of the great equatorial; aperture 5 inches; T 
flecting solar eye-piece with power of 109. 
At the School of Science Obesryatory there were six observ" 
ers, VIZ: : 
5. Professor C. F. Brackett (in charge of the photographie 
operations). He observed the contacts with the equatorial ° 
the S. S. Observatory; aperture 94 inches, which was real 
to 5 inches at all the contacts except the first. The bal 
was a Merz polarizing helioscope, with magnifying powe? 
164. 
