ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



1099 



Fig. 248. 



freedom of manipulation. Work may be carried on rapidly, the 

 balsam yielding at once to tbe sustained temperature of the needle, 

 which moves freely through it, and imparting its heat to the tiny 

 crystals enables them to be turned and examined with much ease. 



Griffith Turntables.*— Mr. E. H. Griffith describes two more of 

 his turntables. 



The first was described Vol. IV. (1884) p. 826, but has now been 

 improved, and as improved is thus described by Mr. Griffith (figs. 248 

 and 249) :— 



The centre of the table, marked with the circles, has a straight 

 spring attached to it beneath. The 

 slide being placed between the two 

 pins A and B in this centre, is 

 partially rotated against tbe spring 

 and pushed forward, when the 

 spring keys it between the two pins 

 and a third fixed pin D at the upper 

 side of the slide, centering it per- 

 fectly for width. The fourth pin E 

 at the left end, 1^ in. from the 

 centre, is for length, and allows the 

 slide to be always placed in the 

 same relative position. The recent 

 improvements add much to the value 

 of the table. One of them is a 

 countersunk decentering wheel and 

 pin C, which may be seen at the 



upper right-hand side of the slide. The axle of the wheel passes 

 through the table and is furnished underneath with a short bar with 

 which the decentering wheel may be turned, forcing the pin against 

 the slide, pushing it as far out of centre as may be desired. Another 

 improvement is in making the end-pin a screw, which may be turned 

 down out of the way if desired. 



The second (fig. 250) presents the peculiarity that the spindle is 

 hollow, for illuminating the centre of the slide for mounting purposes. 



The table has two grooves A and B, milled across the upper 

 surface, equidistant from the centre E and tending towards a common 

 point beyond. To these grooves are fitted two followers, and to the 

 followers are fastened two thin narrow brass plates C and D, parallel 

 to each other, and which are the slide-holders. The pin E is a small 

 screw, which may be turned back out of the way or used as an end- 

 pin, it being 1^ in. from the centre of tbe table. The slide may be 

 placed between the two plates C and D and made to abut against the 

 end-pin E. Then if C and D are pushed the same distance in the 

 direction of E they will clamp tbe slide firmly and centre it perfectly 

 for width. If it be desired to decentre the slide, one of the plates 

 must be pushed farther than the other. 



Some years ago General William Humphrey, of Jackson, Mich., 



* Proc. Araer. Soc. Mior., 8th Ann. Meeting, 1885, pp. 112-3 (2 figs.). 



