470 MANIPULATION. 



Hipparchia Janira (Common meadow brown butterfly. — 

 This test was first shown in this country by Amici, in 1844, 

 by his object-glass of large angular aperture, before described 

 at page 466. Fig. 1, plate vii., exhibits one of these scales 

 magnified 500 diameters ; on it may be seen longitudinal striae, 

 with a number of brown spots of irregular shape ; when the 

 magnifying power is increased to 1,200 diameters, the brown 

 cells are made more evident; but the strias are, in a great 

 measure, obsctired by them, as shown in plate viii., fig. 7. 



Pontia Brassica (Common cabbage butterfly). — This scale, 

 like that of the H. janira above noticed, is provided at its free 

 extremity with a brush-like appendage ; when magnified 500 

 diameters, it presents the appearance shown by plate vii., fig. 2 ; 

 the strise seen on it are longitudinal, which, with this power, 

 appear to be composed of rows of little squares or beads ; 

 when a power of 1,200 is employed upon them, the striae have 

 between them elongated dots or cells, probably of pigment. 

 Fig. 5, plate viii., represents a portion of fig. 2 magnified 

 1,200 diameters ; and fig. 6, in plate viii., a portion of one 

 of the coarse scales from the same insect viewed under similar 

 circiunstances. 



Polyommatus Argiolus (Azure blue). — One of the delicate 

 scales from this beautiful insect is shown at fig. 3, plate vii., 

 magnified 500 diameters ; it exhibits under this power both 

 longitudinal and transverse striae, the latter being much more 

 delicate and difficult to detect than the former. This scale 

 forms a very good test of the defining power of a quarter of 

 an inch object-glass. 



Scales of Podura (Common springtail). — The body and legs 

 of these tiny creatures are covered with scales of great deli- 

 cacy ; according to Mr. Pritchard,* their value as test objects, 

 for the high powers of the microscope, was discovered by the 

 late Mr. Thomas Carpenter, of Tottenham, whilst making 

 some experiments with a plano-convex jewel lens, adapted 

 as an object-glass to a microscope, provided with a Huyghe- 

 nian eye-piece; since his time they have been employed, 

 even up to the present period, as tests for the higher powers ; 

 * Microscopic Cabinet, p. 150. 



