M. Euler on the Perfection of the Microscope. 233 



Art. VIII. — On the Perfection of Microscopes. By Leo- 

 nard Euler. Communicated by Dr Goring. 



J.HE best microscopes which have hitherto been made are yet 

 subject to such great defects that we have reason to be sur- 

 prised that the most skilful artists have not been able to 

 free them from those defects, while they have worked with so 

 much success at the perfection of the telescope. In the first 

 place, we remark generally in microscopes, the great defect, 

 that they represent objects with less distinctness than telescopes, 

 which would be entirely rejected if they exhibited such a 

 great degree of confusion as we are accustomed to suffer in mi- 

 croscopes. And we must admit that the more we increase the 

 amplification of microscopes, the more the confusion is in- 

 creased, so that we can distinguish almost nothing in them. 

 The two sources of confusion, the one being the aperture 

 of the lens, and the other, the different refraction of the beams, 

 concur equally to render insupportable the confusion with 

 which microscopes represent objects. 



The best method of diminishing this confusion, would be, 

 without doubt, in diminishing the aperture of the object-glass; 

 but then we! should lose in clearness, which is generally so 

 little, that in great magnifying powers it is almost impossible 

 to distinguish the different parts of the object under examina- 

 tion. 



It is also a very great inconvenience in microscopes, espe- 

 cially in simple ones, that we are obliged to approach so near 

 to the objects to put them in the focus of the object-glass ; be- 

 cause if there is any inequality in them, it is absolutely impossi- 

 ble to recognize the points which are a little out of the focus. 



The surest means of remedying all these defects will be, 

 without doubt, to employ, as in telescopes, compound object- 

 glasses of different kinds of glass ; and for that purpose, tin- 

 last object-glass in which we have introduced the new species 

 of flint-<;lass which produces a great dispersion of the rays, 

 furnishes us with a method well fitted to carry also the micro- 

 scope to the highest degree of perfection, as it will be easy 

 for a skilful artist to execute such object-glasses which would 



