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practical difficulties are involved which render the scale so determined not 
strictly reliable. Accordingly, the best estimate of scale, when this method 
is employed, may be regarded as derived from the picture itself, that is, 
from the measurement of the photographic disc. Inasmuch, however, as 
this disc is enlarged by photographic irradiation, it is manifest that an 
element of uncertainty is introduced, the amount of irradiation being 
variable under varying conditions. In the American method the focal 
image is used to give the photographic picture, and thus the scale of the 
picture is known at once, since it depends merely on the focal length of 
the object-glass. The centre of the photographic solar disc is determinable 
with great accuracy, no matter how great or how small the extent of 
photographic irradiation may be ; so, also, the centre of the disc of Venus is 
accurately determinable, and hence in this method the distance of Venus 
from the sun’s centre can be determined independently of the photographic 
peculiarities of the picture. The American astronomers maintain that their 
method is very much more trustworthy than the other, and their opinion 
would appear to be confirmed by the experiments on photographic irradi- 
ation which led Lord Lindsay to adopt Professor Winlock’s method in 
preference to Dr. De la Bue’s. 
Observations of the Transit at Cape Town. — Mr. Proctor has pointed out 
that observations of the middle of the transit at Cape Town — directly, and 
by the two photographic methods just described— would have great value, 
and might — if weather proved bad at the few other southern stations — 
become of paramount importance. Venus will be thrown farther from the 
sun’s centre, as seen at Cape Town, than at any other station. It is to be 
hoped that no opportunity really available for the effective observation of 
the transit will be thrown away ; and though we do not hear of any 
measures at Greenwich for employing this method, it is still possible that 
the authorities there are preparing to avail themselves of the suggestion. 
Continued Observations of the Companion of Procyon. — Otto Struve, at 
the May meeting of the Astronomical Society, described the observations 
made at Poulkowa upon the small companion of Procyon ; not the old and 
comparatively well-known companion, as some appear to suppose. After 
presenting the details, he sums up the result as follows : — 
11 If we take the mean values from my observations for the two years, we 
have /y 0 
1873, March 28 d= 12-49 P = 87-65 
1874, April 10 11*67 96-65 
or, after applying the systematic corrections : 
// o 
1873, March 28 d= 12-49 P = 90-24 
1874, April 10 11-67 99-60 
u The distance in the interval would, therefore, seem to have diminished 
by about 0"*8. But owing to the difficulty of the measures, the mean 
values themselves must be subject to such uncertainties that the reality of 
the apparent diminution must be considered doubtful. But in regard to 
the increase of the position-angle, there can scarcely be any doubt. Not 
only does the observed increase of 9°-5 correspond to a considerable linear 
