ee 
4 
a 
LE 
a 
a 
9 
i 
a 
4 
ES 
ef 
: 
é 
D. P. Todd—The Solar Parallax. 491 
Art. LIX.—The Solar Parallax as derived from the American 
_ Photographs of the Transit of Venus, 1874, December 8-9; by 
. P. Topp, M.A., Assistant in the Office of the American 
Kphemeris and Nautical Almanac. 
HirHERtTO no value of the solar parallax has been derived 
from the observations of the transit of Venus made at the 
American ‘stations in 1874. 
In the volume of observations recently issued, Part the First, 
General Discussion of Results, are given most of the data which 
are necessary for the derivation of the solar parallax from (1) 
the photographs of the transit, (2) the optic observations of the 
transit. We shall concern ourselves only with the photo- 
graphic results: these are presented in pages 104-117, in very 
nearly the form of equations of condition involving the correc- 
tion of the difference of right ascension of the sun and Venus, 
the correction of the difference of declination of the sun and 
Venus, and the correction of the assumed value of the solar 
parallax. The residual differences, (O.—C.), being given in 
distance, s, and in position-angle, p, every photograph furnishes 
two distinct equations of condition. e total number of 
photographs is two hundred and thirteen, distributed among 
the several stations as follows :— 
THE NORTHERN STATIONS. THE SOUTHERN STATIONS. 
Wladiwostok 13 Kerguelen 8 
Nagasaki 45 Hobart Town 37 
Peking 26 Campbelltown 32 
Queenstown 45 
Chatham Island 7 
values having bee ted in several cases 1 
corrections arising from the absorption of the solar and the 
g 
103. The first and the second effects being supposably small and 
acting contrariwise on the solar parallax, we may, without very 
great uncertainty, disregard their combined action. The third 
correction should be investigated independently from the 
uations of condition themselves; and this again cannot 
advantageously be done until the definitive longitudes have been 
obtained: all the effects of absorption of the solar and the 
bi etalon atmospheres may then be most opportunely consid- 
ere 
