254 Dr. Goring's Commentary on 



some more light would have been exceedingly acceptable. Now 

 in the Gregorian construction, the primary image is magnified 

 by means of a reflecting engyscope, so that, in fact, we see only 

 the image of an image. The power of the said engyscope was 

 of course equal to that of a lens of -^ of an inch focus, in the 

 4 inch telescope, and ^ in the other, for such would have been 

 the focus of the magnifiers necessary to give the said power of 

 120, had the telescopes been of the Newtonian form. Now, 

 if we would get on at this rate with the larger telescopes, there 

 would be no end to their magnifying power, but unfortunately 

 the larger they get, the worse they get. It has not yet fallen to 

 my lot to see a Newtonian of 7 feet focus bear a lens of less 

 than J of an inch focus (giving a power of 504), with the 

 same distinctness with which the small Gregorians bore a ^^ 

 and J^ It is, however, truly wonderful that human art should 

 indirectly be able to form a picture of such extreme beauty and 

 truth, as to bear the dilatation of a lens of ^ of an inch, or 48 

 times its natural magnitude, without betraying coarseness and 

 imperfection ; other pictures and works of art, produced by 

 the direct operation of the human fingers, seldom bear to be 

 looked at with a lens of less than 1 inch focus: of this nature 

 are some highly finished Dutch pictures, engravings on seals, 

 &c. I have, however, seen the Lord's prayer in a circle -J of 

 an inch diameter, which bore a lens of J an inch focus pretty 

 well. 



Now, I heartily wish I could say that the images formed by 

 the metals of the Amician, or the object-glasses of the apla- 

 natic engyscopes, would bear as much amplification as those 

 of small telescopes, but I am afraid, that (supposing their 

 bodies to be from 6 to 9 inches long) they will not carry 

 a magnifier deeper than i of an inch, without becoming 

 ir\ferior to simple microscopes in the strength and correctness 

 of their vision ; the greater the power of their objective part, 

 the less occasion is there for a deep eye-glass to assist it — and 

 the farther we are enabled to advance in the range of power, 

 without losing the more delicate touches of the picture ; still, 

 however, I am disposed to think that those yet made, are at 

 their maximum of effecliveness, with a power about equal to 

 that of ^V of an inch (240), and if made to exceed it on such 



