282 optics. 



Ellis's single, or agnatic microscope, takes its 

 name from Mr. John Ellis, author of An Essay 

 towards a Natural History of Corallines. By this 

 instrument he was enabled to explain many singu- 

 larities in the economy and construction of these 

 wonderful productions of nature. 



To the practical botanist this instrument is re- 

 commended by the authority of Mr. Curtis, author 

 of the Flora Londinensis. It is simple in its con- 

 struction, easy in it use, and very portable. 



K (Fig. 10.) is the box which contains the whole 

 apparatus : on the top of the box there is a female 

 screw, for receiving the screw which is at the 

 bottom of the brass pillar A, and which is to be 

 screwed on the top of the box K. D, a brass pin, 

 which fits into the pillar : on the top of the pin is 

 a hollow socket, to receive the arm which carries 

 the magnifiers : the pin is to be moved up and 

 down, in order to adjust the lenses to their focal 

 or proper distances from the object. 



In the representation of this microscope, the pin 

 D is delineated as passing through a socket at one 

 side of the pillar, A : it is now usual to make it 

 pass down a hole bored down the middle of the 

 pillar. F is the box which carries the magnifying 

 lens : it fits into the socket X, which is at the top 

 of the pillar D. This arm may be moved back- 

 ward and forward in the socket X, and sideways 

 by the pin D, so that the magnifier, which is 

 screwed into the ring at the end F of this box, may 

 be easily made to traverse over any part of the 

 object lying on the stage or plate B. F is a po- 

 lished silver speculum, with a magnifying lens 

 placed at the centre of it, which is perforated for 

 this purpose. H, is a brass semicircle which sup- 

 ports the mirror I j the pin R, affixed to. the semi- 



