262 Transactions of the Society. 



out any further trouble. This description is correct for the £-inch 

 objective, and all lower powers used with an eye-piece, but may, 

 possibly, have to be reversed with higher powers. 



In conclusion, I should like to add that particular care must be 

 taken in fitting the nose-piece, so as to secure the true horizontal 

 alignment of the apertures when the stop is revolved from one side 

 of the optic axis to the other. If the apertures are not truly 

 aligned, the finished prints will not superimpose properly, and will 

 not be clear and sharp. I may, perhaps, also mention that my 

 only trouble has arisen from a difficulty in obtaining equal illu- 

 mination of both pictures with transparent objects by transmitted 

 light, but as my photos have been taken without an optical bench, 

 this difficulty may not arise when one is used. 



EXPLANATION OF PLATE XI. 



Foraminifera. Various species from Timor Sea, 50 fathoms, x 25. Mounted 

 by Mr. A. Earland. Photographed with a 4 mm. stop. Beck's 1^-in. objective 

 and No. 1 eye-piece. 



