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POPULAR SCIENCE REVIEW. 
tlie eye will distinguish, faint objects much more readily by 
keeping in the dark a few minutes previously. The observer 
will remark some anomalies in different eyesight • some which 
can distinguish very faint objects are unable to separate a close 
double stay, and vice versa , and in many instances the colours 
of double stars will be judged differently. We need not state 
that a comparatively small telescope, in which the glass is pure 
and the figure polished to the true curves, will be found far 
more useful and pleasant to handle than a much larger one in 
which these conditions are forgotten. The excellence of the 
object-glass is the principal affair, and no beauty of mounting 
will compensate for this want. 
In observing double stars, those which are well separated 
should be scrutinized at the commencement and the distances 
and magnitudes gradually diminished, until the most delicate 
objects which the instrument can bear are arrived at, and for 
which a very clear and favourable sky will of course be necessary. 
The observations of the double and multiple stars are the finest 
test for the performance of a telescope. Thus, commencing at 
the coarse double Delta and Kappa Herculis or Eta Lyras, 
he may ascend to Theta Serpentis and Alpha Can. Yenat. From 
Zeta Ursas Majoris and Beta Cephei he can pass to Gamma 
Delphini and Eta Cassiopeise. Closer still are Alpha Herculis, 
Kappa Cephei, and Mu Cygni. Coming to those which are 
test objects for small instruments we have Gamma Virginis, 
Mu Draconis, Bho Herculis, Zeta Aquarii, &c., whilst on very 
favourable nights the observer may look for Delta Cygni, Pi 
Aquilae, Xi Ursae Majoris, Sigma Coronas Borealis. All these 
stars are visible at the present time of the year, and their 
places marked on a good celestial globe. The amateur 
observer has only to transfer those positions mentally to the 
real heavens, which, with a little practice, will be as simple as 
finding any geographical position on a terrestrial globe by 
knowing its longitude and latitude. 
