Di\ WoUastoii's Microscopic Doublet. 253' 



and engyscopes (every man is, of course, welcome to his own 

 on these subjects). 1 shall here propose some fresh considera- 

 tions of the same nature. I have heard it asserted, that, under 

 certain circumstances, telescopes shew us objects better than 

 we could see them with our naked eyes under the same visual 

 angle. If they do, I do not see why engyscopes should not 

 shew us objects as well as simple microscopes. / think Sir 

 W". Herschel somewhere says, that one of the effects of the 

 enormous light and penetrating power of his reflectors, was to 

 shew him what o'clock it was at a distant church, in a night so 

 dark that he could not have told the hour with his unassisted 

 eyesight, by going up to the building — a circumstance very 

 conceivable, if the intrinsic brightness of the visual pencil of the 

 telescope exceeded that of the cylinder of rays taken in by the 

 iris proceeding from the clock, at the distance at which it could 

 be conveniently viewed. 



I have often amused myself by placing some object, on a 

 clear day, so near ?ne, that there should be no sensible quantity 

 of atmosphere to look through (about 30 or 40 feet distant), 

 and viewing it with a fine telescope, charged with an eye-glass 

 of moderate depth, and afterwards going up and looking at it 

 with a pair of spectacles, under the same angle at which I 

 viewed its image in the telescope, and have been astonished at 

 the perfect resemblance of the copy to the original, and this I 

 conceive to be analogous to comparing the action of a simple 

 microscope, against an engyscope of the same power. I think 

 any unprejudiced person making the same experiment would 

 be compelled to admit, that he saw as well with the telescope 

 as with the spectacles, provided always, that the image of the 

 telescope was but moderately amplified. The degree of ampli- 

 fication, which the images of small perfect telescopes will bear, 

 is often very great. I have seen a Gregorian of 4 inches 

 focus, and 2 inches aperture, and another of 5 inches focus, 

 and 3 inches aperture, by Cuthbert, both of which bore a 

 power of 120 with absolute distinctness *, though, of course, 



* The iins^ given of a star of the first magnitude was quite round and very 

 small, with a few faint rings about it — (the result no doubt of the immense angle 

 of aperture : for Mr. C. says, that if he had made the telescopes of the same aper- 

 ture and a longer focus, he should have been utterly unable to preserve the small 

 round artificial disc) — I may remark, that the power of 120 was that to which the 

 metals were worked perfect, for a Gregorian can only be perfect with one power. 



APRIL— JUNE, 1830. S 



