NEW OBSERVATIONS OF THE PLANET MERCUltY. 445 
absence of both change and color anywhere ; and the sixth, by the immutnbihiy 
of the whole. 
All these characteristics are just what tlie rotation period anJ the kinetic tboory 
of gases would lead us to infer as probable upon a globe of Merr^'irj's size rntntiug r 
he does. Observation thus corroborates inference. 
Two further points are worth noting, the one the brlghlne««! along lliu limb, tbe 
other the shadings at the cusps. 
21. Brightness along Limb, — From some time before to some time nft(>r the 
moment of dichotomy the hmb is noticeably brighter than any other part of the 
disk. The brilliancy is almost invariably confined to a bright line or a narrow Imic; 
and what is curious, it is not always in the centre of the limb, but on ocrasions is 
conspicuous along its southwestern edge while being absent from its middle. I luive 
- 
noted this peculiar position of the illumination at recurrent elongu'tionf^, allhougli 
o 
but once. My written notes are as follo\v 
Sept. 2, '96, limb brightest part of planet; 
14, limb brierht all-round like Moon. 
At another elongation : 
Oct. 16, '96, limb much brighter than rest of disk; 
18, limb, especially S, the brightest part of the disk ; 
20, planet's disk brightest a little in from limb N. 
And at yet another : 
Feb. 6, '97, hmb brighter than rest of planet; 
bright along limb, brightness in a line along limb ; 
disk brightest along central portion of limb ; 
23, very bright along limb ; 
F 
Mar. 2, bridit along hmb 
22. Shadings at the Cusps. — At one or both of the cusps is frequently 
a shading, especially when the phase is a cres 
the failure to see the cusps, although it may be d 
This is not, seemingly, a part of 
but apparently is 
produced by a shad 
The effect may last until the planet 
fairly gibbous. See Figs. L 2, 3, 4, 5, 6, 8, 9, Plate XXX.; Figs. 1, 2, 3, Plate XXXI 
and Figs. 1, 2, 3, 4, Plate XXXII. 
23. Albedo. -The look of the planet shows its albedo to be low. For whde the 
markings are more contrasted with their surroundings than is the case with Venus 
-with which body it is best to compare Mercury, -- the general reflective power ot 
the planet's surface i.s much less. This appeared passim in the course of the obscrva- 
