1 EVENINGS AT THE MICKOSCOPE. 



What we see, then, is a perfectly " traiishicent cyl- 

 inder, having a light brown tinge, and marked with a 

 great number of delicate lines, having a general trans- 

 verse direction, but very irregularly sinuous in their 

 individual courses. These lines we perceive to be on 

 the surface ; because, if we slowly turn the adjustment- 

 screw, the lines grow dim on the central part of the 

 cylinder, while those parts that lie near the edges (speak- 

 ing according to the optical appearance) come into dis- 

 tinctness. Presently the edges of the cylinder become 

 sharply defined, and are seen to be cut into exceedingly 

 shallow saw-like teeth, about as far apart as the lines ; 

 these, however, are so slight that they can be seen only 

 by very delicate adjustment. We go on turning the 

 screw, and presently another series of transverse lines, 

 havinir the same characters as the former, but differing 

 from them individually, come into view, at tlie sides 

 first, and presently in the middle, and then, as we still 

 turn, become dim, and the whole is confused. In fact 

 our eye has travelled, in this process, from the nearer sur- 

 face of the hair, right through its transparent substance, 

 to the farther surface ; and we have seen that it is sur- 

 rounded by tliese sinuous lines, which the edges — or those 

 portions of the hair which would be the edges, if it were 

 split through the middle (for, optically, this is the same 

 thing) — show to be successive coats of the surface, sud- 

 denly terminated. If we suppose a cylinder to be 

 formed of very thin paper, rolled up, and then, with a 

 turning-lathe, this cylinder to be tapered into a very 

 lengthened cone, the whole would be surrounded by 

 lines marking the cut-through edges of the successive 

 layers of paper ; and, owing to the thickness of the 

 paper not being mathematically ecpial in every part, 



