958 



SUMMARY OP CUKRENT RESEARCHES RELATING TO 



apparatus to the body-tube of the Microscope, into whicb it is slipped 

 as far as the lower end of the drum A. 



BC 



D 



E 



Fig. 151. 

 F 



a 



7 5 701 



50 



Fig. 152. 



I I I I I I 



The comparison prism with its illuminating mirror is not shown, 

 though the latter is indicated in fig. 149 by dotted lines. It is turned 

 away from the slit by the lever-arm shown in fig. 150. 



Engelmann's Micro -spectral 

 Objective.* — This (fig. 152) was 

 made by Dr. Zeiss for examina- 

 tions by Prof. T. W. Engelmann's 

 Bacteria-method. 



It consists of a plane mirror, a 

 slit, a collimator lens, and a direct- 

 vision prism. The whole apparatus 

 is 77 mm. long, and is applied be- 

 neath the stage, ordinary objectives 

 according to the size of the spec- 

 trum desired being screwed on at 

 the top to project a spectrum at the 

 plane of the object under examina- 

 tion. Both sides of the slit are 

 moved symmetrically by the screw 

 with divided drum. This screw has 

 two opposite threads on a common 

 axis, so that the centre of the slit 

 never changes its place. The drum 

 gives the width of the slit in hun- 

 dredths of mm. The smaller milled 

 head moves outer slides to regulate 

 the length of the slit. 



In place of the prism a grating 

 can be used, which would give an interference spectrum. 



Mayall's " Stepped" Diagonal Rackwork.— Mr. J. Mayall, jun., 

 has suggested the application to the coarse adjustment of a " stepped " 

 diagonal rackwork for increasing the smoothness of the motion. 



n « ^^^ 1^^"^ Journal, ii. (1882) p. 661. Bot. Ztg., xv. (1882) pp. 419-26 



^tqqI:^" K^"S^^''^ ^^''li- f- d- gesammt. Physiol., xxvii. (1882) p. 464, xxix. 

 (,iooo) p. lis. 



