NEW 0I3SERVATI0XS OF THE PLANET MKRCU1:Y. A 
apparently too small. . . . The most natural conclusion is that the reduction fnun 
the limb of the planet or the observed centre of light, to the true centre un^ 1<.(> 
small by an amount which, at the mean distance of the Sun, must Lave hxn neailj 
or quite a second of arc (cf. § 3). The adopted scmidiamctcr 3".4 fiooma so well 
established, both by micrometric measures and by liellomcter measures during frnnplis 
of Mercury, that such a correction to the diameter seems inadmlssiblo." 
Now if we employ the data given by the measures I liavc just discu^J^O'l instead 
of those of previous ones, we shall see that the discrepancy lie noticed in Mercury '• 
right ascension is accounted for. 
Taking the hitherto received value for the diameter and appl^IuK lils formuln, 
we get five twelfths of 3".34, or 1".39, for tlie correction froui fix; centre of light to 
the centre of the disk at the time of dicliotouiy. 
Now from the present study of the planet we wee, first, tlint at the time uf 
theoretic dichotomy there is a loss In addition to the phase loss along the torniiuntor 
due to the loss of the cusps (Art. 37), and that this amounts to 10°. This !- -• is 
represented hj A B in Fig. 1 of the diagram in Article 36. 
It is the sine of 10' into 3".77, or 0".65. 
This is the first part of the correction ; there is a second. Subtracting 0".C5 from 
3".77, we cret 3".12 for the diameter of' the disk actually seen. Now at the time of 
theoretic dichotomy this disk was not a half-moon, as theory supiio.es, but a rrr^ccnt, 
of which the centre of light by Newcomb's formula would lie in consequence not 
five twelfths of the way, but about halfway to the hmb. Dividing tbcrefore .7M2 
by 2, we get 1".56 for the second part of the correction, u Inch, added to 0".C5, n.akcs 
2".21 for the whole correction from the new data. The difference of 
nations for the correction from the centre of light to the centre of liic d.^k is 2".21, 
less 1".39, or 0".82. Now 0".82 is very nearly the discrepancy to be accounted for. 
i± General Discussion of Measures. - We shall now proceed to a general 
discussion of the measures; beginning by taking up Table VI, and then Tables lA. 
and XII. In Table VI. Is given the ratio of the equatorial to the polar d.ameter, 
first as observed in the drawings, and secondly as measured micrometncally, uncor- 
rected; in Table XI. the ratio between the same diameters of the nucrou..ter 
measures for different irradiation corrections at and near the tune of dichotomy ; m 
f(] fonntonai to 
Table XII. the ratios of the micrometnc 
d 
of the 
d p 
If we study the columns ot the various phase ratios, angles, arul .lilT.rcnccs, ^vc 
shall become aware of some curious results. 
