ULTRAMICROSCOPY AND ULTRAMICRO- 

 SCOPIC PARTICLES 



By H. THIRKILL, B.A., B.Sc. 



Clare College, Cambridge 



Introduction 



It follows from a passage in Seneca, that the ancients knew 

 that when writing is observed through a globe of water the 

 characters appear of increased size. The action was attributed 

 to the water and the effect of the glass was not suspected. 



In 1285 Salvino d' Arnato degli Armatii, of Florence, dis- 

 covered the art of glass working and of manufacturing spectacles. 

 The lenses first constructed were of slight curvature, being 

 intended only for spectacle glasses. By successive steps 

 improvements were introduced ; the curvature was made greater 

 and greater, the lens at the same time becoming smaller. Thus, 

 by gradual stages, lenses came to be used as magnifying-glasses 

 and simple microscopes. Dr. Henri Van Heurch makes mention 

 of the existence of an engraving, copied from a picture by 

 Raphael, dating back to 1513-20, in the Palais Pitti at Florence, in 

 which Pope Leo X. is represented looking at some miniatures 

 with the assistance of a magnifying-glass. 



The first microscope was called by the name of " vitram 

 publicanum." It consisted of a small cylindrical box, the 

 magnifying lens set at one end ; at the other, two pieces of 

 glass between which was placed the object to be examined — 

 usually a flea. There was also a " seed microscope," used 

 for observing seeds. 



Another form consisted of a magnifying-glass mounted on 

 a foot, with a needle point at a short distance from the lens ; 

 the object was placed on this needle. The microscope of the 

 savant Leeuwenhoeck was a development of this : there was 

 a greater perfection in the lenses, and the needle carrying the 

 object was of adjustable height. The magnifying power 

 obtained was much higher, in some cases being as high as 



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