452 
NEW OBSERVATIONS OF THE PLANET MERCURY. 
E 
ft 
before discussing them 
accurate as the measures 
evident at a gl 
This is a point worth 
that the drawing 
because of a very gener 
but quite unfounded prejudice towards pinning one's faith to measures. As a matter 
of fact both measures and drawings depend upon eye estimates, and which of the two 
thy is a question of the kind of estimate involved 
3 
first 
the micrometr 
Diameters too Small 
of the polar d 
Th 
measur 
3S to be discussed 
d the first result indicated 
by them is that the hitherto received value of the planet's diameter is apparently mucl 
too small. Instead of giving the value 6".68 for 
1 
the diameter at distance 
measures make the polar diameter at that distance, after all correction had been 
taken 
V'M 
33. Explanation of it. 
produce 
They do 
Not only d 
measures state this definitely, but they 
what 
to account for the smallness of 
P 
deter 
may seem an 
Measures of Mercury h 
pected manner 
be 
(2) upon the planet as affected by phase, inasmuch 
made, either (1) upon the planet 
Now the present measures 
(T 
s 
appears smaller than it 
that in both these 
the planet necessarily 
is: 
through relative invisibility of 
the first case, through irradiat 
m 
the 
nd 
cusps 
W 
o 
d to the irradiation, th 
have 
qiient loss of apparent size at transit speaks for itself; the present 
lowever, somethmg to say about its amount, as we shall see presently. With regard 
of 
through relative invisibility of 
cusps, the m 
established 
