THE president's ADDRESS. 365 



to five or six feet ; now long extension bellows arc inconvenient 

 to use, for you require one, if not two, intermediate frames to 

 support the bellows, and tbese frames require continual atten- 

 tion during the extension or the closing of the bellows. 

 Bellows, however, possess another disadvantage which is of 

 greater importance, viz., that unless the bellows are consider- 

 ably larger than the plate you will be troubled with internal 

 reflections. The wooden tubes can, moreover, be extended and 

 closed in a quarter of the time required for the bellows. 



There is yet one other point in favouir of this apparatus, viz.. 

 its range of power. The plate can be removed a distance of 

 six feet from the eye-piece, its range, therefore, in that direc- 

 tion is ample ; but it is also capable of performing very low 

 power work, such as is quite impossible with some kinds of 

 photomicrographic apparatus. 



To effect this the back is alone used, the trough being re- 

 versed and the microscope connected to the camera by a cloth 

 tube. On looking over my note-book, it appears that the 

 lowest power there was occasion to employ was 85- diameters. 



All the points in the construction of this apparatus have 

 been gone over, and the differences which exist between it and 

 other designs, as well as the reasons for those differences, have 

 been explained. 



Your time has been trespassed on too long, but you should know 

 that this apparatus, which was made by Mr. Baker eight years 

 ago, has worked without a single hitch, and I cannot conclude 

 without expressing my obligation to Mr. C. L. Cur ties for the 

 kind manner in which he superintended its construction, as 

 well as for several valuable suggestions. 



Gentlemen, I will detain you no longer, but thank you for 

 your kind attention to this rather dry subject. 



JoDRN. Q. M. C, Sekies II., No. 34 26 



