386 
POPULAR SCIENCE REVIEW. 
ingenious methods the observer who is using the telescope is 
placed in a kind of cage, suspended in the air from the mount- 
ing of the telescope and carried up and down along with the 
instrument. 
To this day this giant telescope of Lord Bosse’s retains its 
position as the greatest telescope in existence. In its enormous 
size it has still no rival, in its massiveness and weight it is long 
likely to retain its preeminence. 
Which is the most powerful telescope in existence ? 
Lord Bosse’s giant telescope, of course will be the answer of 
most people; it will be the answer of the great majority of 
scientific men ; it would be almost the unanimous answer of the 
British Association, of that Section A which is supposed to keep 
the world informed of the great achievements of astronomy and 
of optics. 
Is this the true answer ? — No. 
To most people, to most scientific men, this answer will come 
like a shock, for to them it has long been a cherished tradition, 
an article of faith, almost an axiom, that Lord Bosse’s giant 
telescope was the most powerful telescope in existence. To 
those astronomers who are observers, astronomers not stargazers, 
it is well known that for years this giant telescope of Lord 
Bosse’s has been beaten in power by far smaller and more com- 
pact rivals. In fact, it is doubtful whether in real power it 
is much superior to its smaller companion,- the three-foot 
telescope. 
There are many who judge a telescope by its size alone, who* 
compute its excellence by aid of a two-foot rule and a know- 
ledge of its cost in pounds. With them a telescope with a 
metallic speculum weighing four tons and measuring six feet 
in diameter, with a tube fifty feet long, and costing a thousand 
pounds, ought to give so much light, have such and such se- 
parating power, and show this or that object.' It is true with 
small telescopes a great deal may be done in this way, but ex- 
perienced observers know that the real power of a telescope can 
only be ascertained by a study of what it has done. Tried by 
this test, the giant telescope of Lord Bosse breaks down. It 
has not the accuracy of definition which constitutes the real 
power of a telescope, for it is mainly upon this that depends 
its capability for doing work. Compared with the metal specula 
which were made at the time when Lord Bosse’s telescope was 
constructed, the great speculum of Lord Bosse’s instrument 
might come out with credit. But great improvements have 
since then been introduced into the manufacture of reflecting 
telescopes, and the present silver-on-glass reflecting telescopes 
successfully rival the finest achromatic telescope in definition 
and in power. 
