APPENDIX I. 253 



The focal plane of the microscope coincides at all times with 

 that of the underside of the cloven foot, so that no focussinir is 

 iiecessary. 



The optical system is contained in a single tnbe, and niay be 

 removed as a sepai'ate unit. The ^ield and object glasses and the 

 graticule are held in the tube l)y a novel and very simple means 

 (patented) without screws. 



Accuracy of the instrument is gnaranteed within .01 mm. 



Messrs. W. Watson and Sons, Ltd. — Microscopes, ol)jectives 

 aiul accessory apparatus. 



