380 W. Harkness—The Solar Parallax. 
The corrections found at each station to LeVerrier’s tables of 
oh age as represented by the mpaneh Nautical Almanac for 
1878, 
a EN gi 
Cambridge: 3. bio oun + 08079 i 20 
AM SMUDGLOR . ck +0°105 —O'12 
AUD ALO? . sep. go + 0°083 + 0°47 
The correction to the north polar distance, given by the Ann 
Arbor plates, seems to be affected by a systematic error, but it 
is doubtful if its source can be discovered because no details of 
the observations were sent to the Naval Observatory, and Pro- 
fessor Watson, who made them, is now dead. 
The probabie error of a position of Mercury depending upon 
two sets of readings made upon a single photograph is 
. HA. Re. D. 
Cambridge ys +07°570 +07'562 
VY RBRIOICOR oe +0°655 +-0°579 
Ae BOr.. oo oe +0°436 +0°514 
The probable errors in right ascension having been reduced to 
are of a great circle. We may infer from the mean of all the 
stations that the average locus of the probable error of the 
position of the planet in the heavens is a circle whose radius is 
To exhibit yet more clearly the degree of accuracy attained 
by the photographic method, a table is appended, which in- 
i the plates, and shows the number of residuals, both 
in right ascension and north polar distance, which fall between 
00 and just under 0-2, 02 and j der 05, ete. 
tabulating the right ascension residuals it mas been assumed that 
0” 2=0*01, 0’°5=0°03, 1”-0=0°-07, 1’°56=0°10, 2’°0=0*13: 
Cambridge. Washington. Ann Arbor. 
Limits. = 
R. A. N..P.D. R. A. NeeED, R. A. NoDeP. 
0”-0-0"°2 3 5 3 7 11 11 
0°2-0°5 5 6 5 6 16 14 
0°5—1°0 10 : 11 10 29 27 
1°0-1°5 5 + 8 3 wie ¥ 
1°5-2°0 0 2 2 1 3 5 
2°0 and over 2 1 1 3 0 0 
Theory of the Gravitational Methods. 
We begin the consideration of the gravitational methods by 
feng an se me 2 for the solar parallax in terms of the 
earth’s mass. 
