278 HERSCHEL. 
A telescope does not magnify real objects only, but 
magnifies also the apparent irregularities arising from 
atmospheric refractions ; now, all other things being equal, 
these irregularities of refraction must be so much the 
stronger, so much the more frequent, as the stratum of 
air is thicker through which the rays have passed to go 
and form the image. 
Astronomers experienced extreme surprise, when in 
1782, they learned that Herschel had applied linear 
magnifying powers of a thousand, of twelve hundred, of 
two thousand two hundred, of two thousand six hundred, 
and even of six thousand times, to a reflecting telescope 
of seven feet in length. The Royal Society of London 
experienced this surprise, and officially requested Her- 
schel to give publicity to the means he had adopted for 
ascertaining such amounts of magnifying power in his 
telescopes. Such was the object of a memoir that he in- 
serted in vol. Ixxii. of the Philosophical Transactions ; 
and it dissipated all doubts. No one will be surprised 
that magnifying powers, which it would seem ought to 
have shown the Lunar mountains, as the chain of Mont 
Blane is seen from Macon, from Lyons, and even from 
Geneva, were not easily believed in. They did not 
know that Herschel had never used magnifying powers 
of three thousand, and six thousand times, except in ob- 
serving brilliant stars; they had not remembered that 
light reflected by planetary bodies, is too feeble to con- 
tinue distinct under the same degree of magnifying power 
as the actual light of the fixed stars does. 
Opticians had given up, more from theory than from 
careful experiments, attempting high magnifying powers, 
even for reflecting telescopes. They thought that the 
image of a small circle cannot be distinct, cannot be 
