A friend in Pennsylvania writes: “Please give us a description of the
transit of Venus, in THE CHAUTAUQUAN for January.”
We answer with the following:
At a meeting of the New York Academy of Sciences, at No. 12 West
Thirty-first street, on the evening of December 13, Professor J. K.
Rees, of Columbia College, gave the result of his observations of the
transit of Venus, made at the college observatory. A large audience
was present and listened attentively to the lecturer’s presentation of
facts.
“I will only detain the Academy a few moments,” said the Professor, “in
presenting the main points in the observations made at Columbia College
on December 6. Most of the figures I will leave out. The station
occupied was the roof of the unfinished observatory of the college. The
telescope was placed in the southwest corner of the roof. This roof
is extraordinarily strong and solid, the beams being of iron, twelve
inches in depth. Solid brick arches spring from beam to beam. The
height of the roof from the street is about one hundred and ten feet.
The walls supporting the roof are four feet thick. An unobstructed view
was had of the whole transit. The position of the instrument was only
a few feet from the old observatory, so that we may take the longitude
and latitude of our instrument from the American ephemeris—
Latitude, +40° 45′ 23″.1.
Longitude:—From Washington, -0h. 12m. 18.40s.
Longitude:—From Greenwich, +4h. 55m. 53.69s.
“The timepieces used were a mean time chronometer, No. 1,853, made by
Parkinson & Frodsham, of London, England, and a sidereal chronometer,
No. 1,564, made by Negus & Co., of New York City. The instrument used
in the observations was an equatorially mounted refractor by Alvan
Clark & Sons. Aperture 5.09 inches; focal length of object glass,
74.3 inches. The magnifying powers used were 48 on the first contact,
165 on the second and third contacts, and 95 on the fourth contact.
The telescope was moved by clockwork, supplied with a Bond spring
governor. In making chronometer comparisons the sidereal chronometer
was left at the college and the mean time chronometer was carried to
the instruments on which signals were to be received. The sidereal
chronometer has the hours graduated to XII.”
Professor Rees had prepared, but omitted to give, an elaborate system
of chronometer comparisons with the Western Union time signals and
the Washington time signals. The object of the comparisons was to
obtain the exact error of the chronometers used at the time of the
observations. The Western Union time signals sound the local mean time
at the City Hall of New York city. The longitude of the City Hall
from Washington is 12m. 10.47s. Mr. Hamblet, in charge of the Western
Union time system, gives the errors of the Western Union time signals
as 1.11s. fast on December 5, noon; 1.35s. fast December 6, noon. The
professor also omitted a table of observations and the times taken down
at the instant by each of four recorders.
“Correcting the observed contact times,” he continued, “the following
table was obtained: