680 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



diameter with bis caliper. Ho then takes another chip, stops, tries, 

 starts, stops, tries, until the subtle and ever-varying sense of feeling 

 satisfies him that ho lias obtained the correct diameter. But, after 

 all, the uncertainty in the setting of the caliper remains, and this 

 uncertainty is generally greater than that which would bo found to 

 exist in the comparative trials of the diameter. If, now, we increase 

 the required unit, and especially if fractional increments are added, 

 the problem of transferring a required length from a scale to a caliper 

 becomes a most serious one. 



" Only one other objection remains to be overcome. It is the 

 common impression that the delicate adjustments of the Microscope 

 which are continually demanded — especially the adjustment for focus 

 — can only be made by the most delicate and sensitive means. No 

 impression could be more erroneous. Give me a small lead hammer 

 and I will set the top of my comparator to a given line in half of the 

 time and with greater precision than it can be set by means of a 

 screw movement. Give me a vertical movement by means of an 

 eccentric disc and a long lever arm, and I will bring the surface of a 

 plate weighing 100 lbs. into the focus of the objective quite as quickly 

 and quite as accurately as a similar adjustment could be made in the 

 hands of a professional microscopist." 



Klonne and Miiller's Diaphragm. — Herren J. Klonne and 

 G. Miiller have patented * an ingenious diaphragm shown in 

 figs. 129-133. 



It consists of two plates, each pierced with an aperture as shown in 

 figs. 132 and 133. They are connected to a T-piece g by pins passing 



Fig. 129. 



Fig. 130. 



Fig. 131. 



through the slots in the ends of the arms. This T-piece is attached 

 to a frame sliding below the condenser, and just wide enough to allow 

 of the plates moving backwards and forwards in grooves as the 

 T-piece, turning on a central pin, assumes the different positions shown 

 in figs. 129-131. In the first position the light is shut off, while in 



* German Patent, Kl. 42, No. 31870, 2Gth August, 1885, 1 p. and 11 figs. 



