1/4 



THE AMERICAN MONTHLY 



[September, 



meter with the meters of the archives 

 will appear in the Transactions. 



In recognition of the courtesy of 

 the Royal Microscopical Society in 

 having honored the American society, 



by making its President for the time, 

 a Fellow ex officio, the President of the 

 Royal Society was for the time made 

 an honorary member of the American 

 Society. 



( To be Continued. ) 



Fjc. 31 — Zeiss SrBcrno-PoLARiznR. 



Zeiss Spectro-Polarizer. 



The instrument manufactured by 

 Mr. Zeiss, under the above name is a 

 modified form of the Spectro-Polari- 

 Microscope of Rollett, already de- 

 scribed in these columns. It is repre- 

 sented in fig. 31, It is intended for the 

 same purpose as the latter instrument, 

 but it can be applied to an ordinary 

 microscope as an accessory. The 

 reader is referred to the preceding 

 article, describing Rollett's instru- 

 ment, for an account of the principles 

 involved in the construction and use 

 of this one. 



It is intended for the study of the 

 double refractive properties of micro- 

 scopic objects. It is placed hori- 

 zontally beneath the stage of the 

 microscope, the light passing in through 

 the polarzing prism (Prazmonoski's), 

 at Fe, ; through the slit Sp. ; the col- 

 limating lens C. ; the two prisms P.P., 

 and finally through an objective at O. 

 to the object on the stage. Selenite 

 plates are j^laced in the j^ath of the 

 rays at G. 



The supplementary tube sk., con- 

 tains a scale, an image of which, when 

 properly illuminated, is reflected into 

 the field of view from the face of the 

 prism, as shown by the dotted lines. 

 This scale gives the wave-lengths of 

 the lines in the spectrum. By means 

 of various adjustments, the spectrum 

 can be made to traverse the field in 

 any direction. There is no doubt 

 much greater dispersion can be ob- 

 tained with the prisms in the Zeiss 

 instrument, than the direct-vision 

 prisms of the Rollett instrument will 

 give. 



