Aplanatlc Ohject-gtasses, 255 



are best adapted for the solar microscope, for they give a full- 

 sized field of view to this instrument, good to the edges, which 

 no single object-glass will do, as I have had occasion to remark 

 in my paper on Mr. Tulley's aplanatics, unless converted into 

 a compound, by means of eye-glasses, &c. This popular and 

 highly amusing instrument will now receive the utmost refor- 

 mation and improvement of which it is capable, and become 

 truly scientific in its construction : hitherto it has been a mere 

 toy, but one degree removed from a magic lantern. 



I shall now allow Messrs. C. to say what they can for them- 

 selves, and to detail the various modifications which they have 

 introduced into their instruments, since they executed Mr. 

 Lister's order, by giving a translation of a letter I have received 

 from them on the subject, and shall conclude by expressing a 

 hope that no national or illiberal feeling has entered into the 

 composition of this critique, and that I have used my oil, 

 vinegar, and pepper in correct proportions. 



** Paris, Oct, 15. 

 " Sir, 



** Accept our thanks for your extreme complaisance in offer- 

 ing to publish the results obtained by us in the construction of 

 microscopes. Since the order executed for Mr. Lister, we have 

 improved those instruments last completed, by greatly enlarg- 

 ing the diameter of the illuminating mirror, in order to obtain 

 still greater light. The prism for opaque bodies is diminished 

 about one half, and by a small modification in its mounting 

 is rendered more serviceable : the diminution of the length of 

 the body has enabled us to augment the magnifying powers by 

 different eye-glasses, and the four double object-glasses placed 

 in a better mounting can be used separately or in super- 

 position, according to the pleasure of the observer, either to 

 form quadruple objectives, or even to combine in a mass toge- 

 ther. This last arrangement produces a great accession of 

 magnifying power, without injuring the clearness of the image 

 or arresting much light. 



*' You see. Sir, that we have the pleasure of coinciding per- 

 fectly in your opinions about improvements, for we adopt the 

 quadruple object-glass as the best, and we give three changes 



S 2 



