60 On the Spherules which compose the Bibs of the Scales 



and a "C eye-piece" magnifying about 200 diameters, the dark 

 colour is seen to be owing to very dark ribs, with bright intercostal 

 spaces — brighter as they approach the quill ; and these spaces 

 appear filled with some kind of structure upon drawing out the 

 tube 4 inches, so as to give about 300 diameters. 



Some of the scales adhere to the under side of the cover, and 

 these are better defined. Inch and a half condenser (direct light), 

 without stops (a very fine Koss objective). 



2. Fine Koss Quarter " 1851." The ribs assume a pale bluish 

 colour, and the pale intercostal spaces a pale rosy hue. This 

 appearance is best seen towards the quill end, and is easily brought 

 out with a delicate fine adjustment.* Aperture of \ 70°. 



An antique |th (|th) of Powell's make (Aperture 60°), with 

 A eye-piece shows the ribs much darker, but clearly beaded. No 

 appearance of rose colour, but a faint bluishness. The scale has 

 been crushed in places, and in the wide gaps of the openings appear 

 very dark clusters of minute bodies, resembling granules, in strong 

 relievo. It is noon, and a cloudy grey day. 



3. Powell and Lealand's fine 1862 dry ]rth, A eye-piece. The 

 ribs are indistinctly beaded, and very dark ; the intercostal spaces 

 light and translucent; the granules indistinct in the broken up 

 spaces. The edges of the quill are somewhat thick and blurred. 

 A few isolated spherules lie in the open spaces, surrounded by a 

 white halo. With the " G eye-piece " and a power of 800, above 

 the bead appears a bright focal point (which demonstrates its con- 

 vexity) ; in concave objects the bright focal point lies below the 

 surface in " dry mounted " objects. 



It appears probable the bead can be measured by finer definition 

 with a good light and Powell and Lealand's new immersion ^th. 



I now substitute a very fine half-inch objective for the 1^-inch 

 condenser in order to get more light. 



The ribs appear narrower, and the intercostal spaces full of 

 some kind of structure, apparently granular, which is still more 

 distinct with condenser formed by the "Koss 1851 " Quarter. 



4. B eye-piece ; Powell and Lealand's new immersion \ih, \ con- 

 denser, dull daylight as before. The ribs appear darker, Indian- 

 ink colour, thinner, sharper, cleaner ; between the ribs (and cross- 

 ways like the rounds of a ladder, only thickly set together) small 

 dark beads are arranged in rows of three spherules in contact. In 

 the broken spaces I perceive a set of trios isolated, still arranged 

 nearly in straight transverse lines, and these spherules appear 

 nearly half the diameter of a rib. At the quill end of the scale 

 the spherules appear fainter. 



* I cannot too highly praise the extreme steadiness and delicacy of the new 

 stand Messrs. Powell and Lealand have specially constructed for me, with a 

 silver-rimmed stage divided to minutes of arc of rotation. 





