296 



Fusion- Structures in Meteorites. 



I found it indispensable to have some contrivance by wliicli the 

 section under examination might be completely rotated, and 

 yet not be thrown out of the optical axis, the Nicols at the 

 time remaining stationary, crossed so as to give a dark field. 



There are various devices to effect this, the most desirable of 

 which is undoubtedly that whereby the whole stage may be 

 rotated ; in my instrument, however, the stage is fixed, so t de- 

 signed a rotation-plate that can be attached or removed as occa- 

 sion may require, without interfering with the regular stage. 

 As the arrangement is very simple and inexpensive, and 

 may perhaps be found serviceable to others^ a brief description 

 may here find place. 



>^ 





F 











^^ OD ~~"~-\ 



^ 







/ / ^ 



C 



B \ \ 







\ \ ^ 



E \^ -^ 



E / / 





i 





^^^^--—^^---^ 



^yjQ 





w 



^--^mr:--^ 





A 



A is the fixed stage, 27 mm, long, 21 mm. broad. [This pro- 

 portion has been slightly altered, to adjust the cut to the page.] 



B is the rotation-plate, 17.5 mm. diameter. The centre of 

 this plate has been cut out, forming a circular hole, C, 5.5 mm. 



