434 Dr. Goring on Achromatic Microscopes^ 



ciently explains the reason of that singular property I have 

 described. 



This is a singular proof of the acuteness of the sense of 

 feeling, for the said teeth may be felt much more easily than 

 they can be. seen. We may thus understand why a razor 

 will cut a hair in two much more easily when drawn against 

 its teeth, than in the opposite direction. 



t 



P. S. The instrument which I have in this paper termed 

 the Amician Microscope is not the legitimate offspring of 

 Amici, (from whom its principle only has been borrowed) ; 

 but an improvement of mine, executed by T. Cuthbert. 

 The profound critical acumen and superior taste of the pro- 

 fessor (as I am given to understand) wholly rejects and 

 disowns the particular modification in question, as a spurious 

 and bastard variety, which must be affiliated upon myself, 

 being wholly different from his in every thing but the optical 

 principle. With this decision I am perfectly content. 



ASTRONOMICAL AND NAUTICAL COLLECTIONS. 



July, 1827. 



i. A Letter from Mr. Henderson, containing a corrected 

 Method of computing an observed Occultation. 



Dear Sir, Edinburgh, 3, Leopold Place, May, 1827. 



I THINK that my Rules for computing an observed 

 Occultation may be improved ; and, in order to enable you 

 to judge of this matter, I beg leave to inclose a copy of the 

 corrected rules with an example. I give the preference to 

 the corrected rules for the following reasons : — 



1. When the star is near the zenith, a considerable degree 

 of uncertainty attends the altitude computed by the method 

 in the Requisite Tables, on account of the small variations 

 in the sines of arcs approaching to 90° : and this uncertainty 

 exercises a considerable 'jafluence upoa the parallaqtic angle 



