110 



lY. — A Metliod of Adjusting Tube Levgth. 



Ey H. Hartridge, M.A., M.D., F.R.M.S., Fellow of King's 



College, Cambs. 



(Read December 18, 1918.) 

 One Diagram. 



Eeside the method of adjiistiDg tube length which has been 

 completely described by Ainslie {!)* there is, I have found, another 

 technique which has certain advantages. This may be described 

 as follows : — With the microscope set ugjn the ordinary way, and 

 with the condenser correctly centred, a slit-shaped aperture cut 

 in suitable material (cardboard, sheet metal, etc.) is mounted 

 beneath the condenser in such a way that the slit may be caused 

 to travel at right angles to its long axis. In this way the beam of 

 light is caused to traverse different p&rts of the condenser aperture. 

 (See diagram.) 



Coiyp&N&ER 



MnvARLt •PlA-PMRAW 



Diac^ram showing position and direction of motion of slit in relationship to the 

 ° aperture of the substage condenser. 



The eye-piece to be emploved is fitted with a pointer, the end 

 of which is near the centre of the field. (For the pointer a stiff 

 hair or bristle will be found suitable.) The eye-piece being placed 

 in the draw tube, the edge of some conspicuous part of the specimen 

 is brought close to the end of the pointer. 



* The italic figure within brackets refers to the Bibliography at end of the 

 paper. 



