250 Dr. Goring's Commentary on 



definite figure whatever to Saturn, will yet be able to draw the 

 light emitted by some distant cluster of stars to a well determined 

 focus, and shew each distinct and separate from the rest, 

 though as close as regular double stars, which it would be ut- 

 terly incompetent to separate. For the same reasons, it will 

 shew faint nebulae nearly as well as if it was a more perfect 

 instrument — upon the same principle, microscopes which, with 

 a faint illumination, exhibit no traces of aberration, shew it 

 strongly when a vivid light is thrown upon the object, whether 

 diaphanous or opaque. It is probably on this account that 

 deep object-glasses and lenses with large angles of aperture, 

 perform better than equally perfect shallow ones of the same 

 penetrating power, which admit a larger portion of light, and 

 thus render their defects more sensible. 



Now, this is what I should suppose Wollaston alludes to in 

 Par. 2, did he not, in the next, speak of collecting as much of 

 the admitted light as can be done, by simple means, to a focus 

 in the same plane as the object to be examined^ (of course, a 

 transparent one is here meant.) 



The practice of condensing light on a transparent object is 

 that which of all others most tends to aggravate the imperfec- 

 tions and aberration of a microscope ; as far as my own expe- 

 rience goes, I have never found it advantageous with any object 

 whatever. The light of the atmosphere procured by directing 

 the body of a microscope against the sky, without the aid of 

 mirrors or lenses, is quite sufficient to any object with which I 

 am acquainted, with by far the greater number, more than 

 sufficient ; even artificial light, if the construction of the 

 mounting permits it to approach near enough to the object, 

 needs no condensation. 



If, moreover, a microscope has no aberration whatever about 

 it, still there is a certain degree of intensity in the light inter- 

 cepted, which is best adapted for exhibiting objects to advan- 

 tage, and this is almost constantly below the standard of bright 

 daylight, which requires qualification by reflection from mir- 

 rors, or by other means, to produce the maximum of distinct- 

 ness of vision. I have perpetually preached against the practice 

 of condensing light on the plane of the object ; for it is obser- 

 vable, that all microscopes possessing concave mirrors, or 



