INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 



337 



turn of tlie screw moves the latter through a certain small distance. 

 One turn of the screw (which has a wheel s attached to it divided into 

 ten parts) moves the carrier 1 mm., and each of the divisionsrepre- 

 sents yL mm., and gives an elevation of ^jj-^y mm. to the ohject. 



In order to be able to place the carrier at any desired point of 

 the instrument, a '* coarse adjustment " is necessary. This is accom- 

 plished by the arrangement shown in Fig. 28, which represents a 

 vertical section of the apparatus taken at the point r of Fig. 27. The 

 piece r is seen to be in two parts, r and r', forming a clamp round the 

 screw « ( = ^ of Fig. 27), and hinged in such a way that, by means 

 of a partly right-handed and partly left-handed screw t, they can be 



Fro. 28. 



separated or brought together. By loosening the screw, the piece r 

 with the object-carrier can bo moved freely by the hand, until the 

 latter rests at any desired point. The piece r can bo screwed up to 

 p (u) again, the instrument being then ready for use as before, (v is 

 a "guide" along which the object-carrier slides.) 



Thin Covering Glass.* — At a meeting of the Section for Micro- 

 scopical Science of the Royal Society of New South Wales, Mr. Hirst 

 is reported to have " exhibited some very thin ghiss suitable for the 

 covering of microobjccts. Tliis glass is simply blown from ordinary 

 glass tubing, is incomparably thinner than the thinnest covering 

 glass, and is so elastic that it is easier torn than broken, and may bo 

 readily cut to any shape with scissors." 



* 'Journ. an.l Pror. Roy. Roc. N. S. Wsilos,' xii. (1S7H) p. 2C2. 

 VOL. III. Z 



