1819.] Mr. Hall's Description of an improved Microscope. 107 



Article IV. 



A Description of an improved Microscope for opaque Objects. 

 By Mr. Hall. (With a Plate.) 



(To Dr. Thomson.) 



SIR, 39, Southamptnn-TCK, March 31, 1819. 



Having spent much of my time lately in microscopical pur- 

 suits, I have found the usual methods of exhibiting opaque 

 objects very defective, in consequence of the want of light and 

 the complexity of the instrument, both of which evils I have 

 taken great pains to remedy; and, I trust, the following improve- 

 ment will be found generally useful, and contribute much to the 

 amusement of those who delight in studying; the works of nature. 

 1, therefore, enclose a drawing and description of the improved 

 apparatus. I am, Sir, your most obedient servant, 



Richard Hall. 



A (Plate XCV) represents the instrument put together ready 

 for use ; it is of a tubular form 3-i- inches in length, and three 

 in diameter, consisting of two lenses at the end * one double 

 convex, the other, plane convex, their combined focus being 

 equal to the length of the tube. 



B represents a sliding door, with an aperture in its centre, 

 moving backwards and forwards by means of a pinion. 



C, a moveable cup, with a scioptic ball and a pair of forceps 

 through its centre, for the purpose of holding and adjusting the 

 object. 



D, a small hole to observe whether the object be in its right 

 place. 



E, a circular piece of brass that screws to the tube, A, having 

 a hole in its centre to receive the nut, F, which is also a circular 

 piece of brass, of 1^ inch in diameter, having three screws ; 

 namely, one male, q q, to screw to E ; two female screws, one, 

 Z z, for the speculum, the other, k k, for the compound body. 



Having thus described the several parts of the instrument, I 

 have only to say a few words with respect to the method of using 

 it. When put together, as at A, it should be screwed to a 

 lantern containing an Argand lamp; then the cap, C, is to be 

 taken off, and the object placed between the forceps ; upon 

 replacing the cap, C, looking through the hole, D, for the pur- 

 pose of seeing that the light be thrown upon the object, the 

 instrument is then ready for use, and is adjusted to its proper 

 focus by turning the pinion . 



^ hen a deeper speculum is required, it is necessary to 

 unscrew E for that purpose. The advantages that this instru- 

 ment possesses over those generally in use may be comprised 

 in a few words; viz. it is most simple in its construction, it 



