MICROSCOPIC OBJECTS. 109 



the candle is so placed as to bring out the latter strongest, 

 and the scale is turned round in the axis of the micro- 

 scope in certain positions, they will cease to appear con- 

 nected. In this object it is the sharpness and clearness 

 of the spaces that chiefly evince the goodness of a mi- 

 croscope ; for the longitudinal lines are easily developed. 

 Another species of this family (Lepismense) — ^namely, 

 the Petrohius mmntimus — found under stones near the 

 sea coast, has longer scales than the former, and very 

 strong cross striee, which afford excellent common tests. 



(2.) " Scales o^Morpho Menelaus. — ^This butterfly is in- 

 digenous to America ; the wings are indented, and their 

 superior surface of a highly-polished blue colour. 



" The imbricated scales from the centre of the superior 

 side of the wing are of a pale blue, mixed with others 

 almost black. The former are mostly broader than the 

 latter, and are the test-objects required ; they measure 

 about the one-hundred-and-twentieth of an inch in length. 

 A\Tien viewed under a microscope they exhibit a series 

 of longitudinal stripes or lines. Between these lines are 

 disposed cross striae, which with the lines give it the 

 appearance of brickwork. 



" The microscope or engiscope under examination 

 should be able to make out these markings with the spaces 

 between them clean and distinct. The cross stricE which 

 give the brickwork appearance are seldom to be seen all 

 over the feather at once. The tissue that covers this scale 

 or feather contains a large portion of colouring-matter, and 

 is often destroyed in removing the scale from the wing. 



