PROCEEDINfir OF THE SOCIETY. 227 



A paper by the Rev. Hilderic Friend on " British Enchjtra3ids " was 

 taken as read. 



Dr. Eyre read a paper by Dr. C. Metz on " The Step Micrometer, 

 with simplified Micrometer Scale," the micrometer itself being exhibited 

 by Mr. Ogilvy. 



In the discnssion following on this paper, the President said that a 

 casnal examination of the micrometer seemed to justify the author's 

 claim that it simplified micrometric observations. 



Mr. Spitta remarked that, so far as he could gather, the method of 

 evaluation was practically the same as in other micrometers, and that 

 the principal improvement consisted in the increased clearness obtained 

 by the arrangement of the step echelon. 



Mr. Ogilvy pointed out that when the valuation was once obtained, 

 only simple multiples remained to be dealt with ; indeed, using ^i^ in. 

 objectives, every division represented 1 /x, and no multiplication whatever 

 was required. 



Mr. Barnard suggested that the chief advantage of this micrometer 

 was the method of spacing, which enabled a reading to be made quickly 

 and with certainty. The distance between the lines had been carefully 

 calculated to suit a particular series of Leitz objectives, but it might, 

 and probably would, happen that other makers' objectives would not so 

 easily adapt themselves, at least without considerable alteration of tube- 

 length. 



Mr. Ogilvy said that in the case under discussion, the valuation was 

 reduced to a simple multiple with any given objective. 



The President said that he regarded the micrometer as one with 

 which, by taking a little prehminary trouble, the optical system could be 

 so arranged that the observer worked with a so-called unity figure with 

 any given objective. 



Mr. Cheshire said that as he understood the matter, Mr. Ogilvy 

 simply proposed to adjust the tube-length, so that the projected length 

 in the image plane should be a simple multiple of the unit of length 

 projected, with the object of minimizing the arithmetical work. Gener- 

 ally speaking, of course, the projected length was not a simple multiple 

 of that projected from the stage micrometer. 



The President thought that in any case, from the practical stand- 

 point, the micrometer would prove to be a useful one. 



A hearty vote of thanks to Dr. Metz and Mr. Ogilvy was passed 

 unanimously. 



The President announced that the next Ordinary Meeting of the 

 Society would be held on Wednesday, April 16. 



The next meeting of the Biological Section would be held on 

 Wednesday, April 2, and the Brass and Glass Section would meet on 

 Wednesday, March 26, at 7 o'clock for 7 . 30. 



