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rOPULAR SCIENCE REVIEW. 
observe the transit of Venus) is a suitable position, and the Eepsold helio- 
metre, with which the transit is to be observed, a suitable instrument. Juno, 
in opposition on November 5, 1874, has a horizontal parallax of 8"*7, and 
•south declination of 3 o, 50'. If we suppose that we may begin to measure 
when the planet has an altitude of 20°, and continue till the altitude is 40°, 
and at setting begin to measure at an altitude of 40°, and observe till the 
planet’s altitude is 20° : then for opposition we have — 
Altitude. 
Parallax in A.R. 
Hour Angle. 
o 
„ 
h m 
20 
7-70 
4 41 
30 
7-05 
40 
6-14 
3 15 
Time available for observation 
1 26 
“ In other words, we shall be able to observe a displacement of about 
14", and have 86 minutes both at rising and setting during which we may 
make observations. 
u The observations can be made with advantage for a month preceding 
rand a month following opposition. 
“ It will not be possible to observe the planet at so large an hour angle in 
"the early mornings a month before opposition, as the sun rises when the hour 
. angle of the planet is about three hours and a half ; nor similarly a month 
after opposition shall we be able to commence observation so early as is 
desirable, and moreover the horizontal parallax will be a little less. Not- 
withstanding this, for fifty nights an average parallactic displacement in 
A.R. of about 12" can be obtained.” 
Variability of Red Stars. — Mr. Birmingham has communicated to the 
Astronomical Society some observations which appear to show that several 
of the stars in Schjellerup’s well-known Catalogue of red stars are variable 
in brightness and in colour. He had already discussed the probable varia- 
bility of No. 252 (which is now invisible). The others which he deals 
with are Nos. 98, 101, 74, 77, 63, 152, and 280. We quote the following 
remarks, as calculated to be of interest to observers : — 
“ I first searched for No. 90 on February 3, 1873, and failed to find a red 
star in, or near its position. I was equally unsuccessful on February 6 
and 8, on September 23, and December 26 ; and on December 28 I wrote to 
Messrs. D unkin and Lynn, of the Boyal Observatory, requesting that it 
might be looked for. This was accordingly done, and Mr. Downing, who 
made the observation with the transit-circle, found, on January 3, that the 
exact position of 90 was occupied by a 7-magnitude colourless star, without 
even a tinge of red. It was afterwards identified as one of Flamsteed’s 
stars, 44 Camelopardali. This star, which I knew, appeared to me rather 
less than the 7th magnitude and of a bluish-white colour. Schjellerup 
notes it as one of the stars in the Dorpat Catalogue, where it is rated at 
• the 7th magnitude and marked rubra j so that it seems to be variable at 
least in colour, if not in magnitude. 
(t No. 101 is taken by Schjellerup from a note by Piazzi, who describes 
it as* red, withoulT'stating the magnitude, and rather roughly gives its po- 
sition as preceding by about 2' another of his stars (No. 187) on the same 
