136 A. ASHE ON TWO-SPEED FINE ADJUSTMENTS. 



The form adopted by Messrs. Beck is seen in the accompanying 

 illustration (Fig. 3). 



It will be seen that the arrangement only differs from my design 

 in having a strong, quick-moving screw (a) in the centre for 

 the coarser adjustment, whilst in place of a central fine micro- 

 meter screw a thread is cut upon the exterior of a cylinder of 

 large diameter attached to the milled head (b), thus reducing 

 wear and tear to a vanishing point and adding greatly to its 

 durability. 



In this form the upper milled head controls the quick screw, 

 which in practice proves to be a more convenient ari'angement 

 than does the converse. 



I have frequently used this form of fine adjustment continuously 

 for many hours, and can testify to its utility under such circum- 

 stances, not only by the saving of time effected, but also by the 

 relief to the eye, brought about by the rapidity with which 

 objects come into approximate focus. 



The two-speed fine adjustment just referred to, and illustrated 

 in Fig. 3, is of course essentially the same as that adopted by 

 Eeichert, in one of his latest instruments (see "The Microscope 

 and its Revelations," 8th edition, pp. 210, 211), but as it was 

 worked out quite independently, and was completed and manu- 

 factured before Reichert's instrument was heard of in England, 

 it has been considered justifiable to include it in this paper. 



In conclusion I wish to express my thanks to Mr. Scourfield for 

 his help in bringing this matter forward. 



Journ. Quekett Microscopical Club, Ser. 2, Vol. VIII., No. 40, November 1901. 



