Z00L0C4\ ANN BOTANY, MICROSCOPY, ETC. 



409 



whether such piece is thicker or thinner than the standard. The scale 

 indicates in thousandths or ten-thousandths, or whatever is desired. I> is 

 an adjusting screw and slot whereby the scale may be adjusted to com- 

 pensate for the variation in the threads of the micrometer. In tig. 47 

 is shown the lever R connected by suitable gearing with the pin A and 

 with the lever IV and the pointer B. The operation will be the same, 

 only tin scale or dial in this case may be more conveniently made liner 

 than in the other case, as for ten-thousand ths or above. The button at 

 B" enables the lever B' to be operated. In either case, if the piece to be 

 inserted should be thicker that] the standard the part B' or B maybe 



\KW 



D-'tc 



Fig. 40. 



Fig. 47 



used to draw down the pin to let the piece in readily, and then when the 

 pin is released it will move against the piece and indicate on the dial the 

 amount t! • piece may be over or under the standard size. 



(5) Microscopical Optics and Manipulation. 



Transmission of Light through Transparent Inactive Crystal 

 Plates, with special Reference to Observations in Convergent 

 Polarized Light.* — F. E. Wright, in his treatment of this subject, 

 divides his treatise into two parts, viz. : Part I., Theoretical ; Part II., 

 Observations and .Measurements. In the first part he develops in terms 

 of the electromagnetic theory of light the general mathematical treat- 

 ment of the transmission of light waves through a transparent inactive 

 crystal plate, special attention being given to the rotatory effects of the 

 boundary surfaces of the crystal plate on the plane of polarization of a 

 transmitted wave. Both theory and the observations of Part II. show 

 that, as a general rule, a nniradial plane polarized light wave after trans- 



* Amer. Journ. Sci., xxxi. (March, 1911) pp. 157-211 (18 figs.). 



