194 MICROSCOPIC OBJECTS. 



sensible mischief, but not eye- and field-glasses, espe- 

 cially the latter.) I gave this megaloscope to the late 

 Mr. Wm. TuUey of Islington, who set very httle store 

 by it, as well he might ; it served to amuse his children, 

 who easily managed it, as, from the great length of its 

 anterior conjugate focus and small size, it might be held 

 in the hand, and did not want a stand. , 



VvTien a megaloscope is properly constructed, and has 

 aU the optical excellencies it should have, its lowest 

 power ^vill be about equal to that of its eye-glass : that 

 is, the image formed by the shallowest objective will not 

 be a magnified one, but of the same size as the object ; 

 consequently it will be capable of taldng m an object not 

 superior in size to the field-bar of the eye-piece, whatever 

 it may be. 



Now as I do not think it is of much use to view 

 objects with a magnifier of less focal distance than 2 

 inches, that power may be pitched upon for the lowest 

 of the megaloscope ; and the instrument I propose to 

 describe has its proportions regulated accordingly. 



a, b, c, d (fig. 1), is the optical part of the megaloscope, 

 2^ inches in diameter and about 14|- inches long, reckon- 

 ing in the eye-hole, which screws on at a, and is repre- 

 sented at fig. 2 ; the eye-glass is 2 inches, the field- 

 glass 4 inches in focus ; the object-glasses are three in 

 number and situated in the part c, d, and may be used 

 together or separately. The object-glass at c is 3^- inches 

 focus ; the other two are of the same focus (4-i inches), 

 and are set in the same cell, giving a combmed focus of 



