422 



On High-Power Definition, 



[June 19, 



XVI. "On a Standard Voltaic Battery." By Latimer Clark, 

 C.E. Communicated by Prof. Sir William Thomson, F.R.S. 

 Received June 19, 1873. 



This paper is a revised version of a paper read last Session. (For 

 Abstract see Proceedings, vol. xx. p. 444.) 



XVII. " Note on High-Power Definition as illustrated by a com- 

 pressed Podura-acale." By E. B. Beaumont, F.R.S., and 

 Dr. Royston-Pigott, F.R.S. Received June 19, 1873. 



Nothing in microscopic matters has ever afforded us such complete 

 satisfaction as the following result of a very fine definition, accom- 

 plished by means of a Grundlach German ^ immersion lens, corrected 

 by a new method, which Dr. Pigott at present delays publishing in 

 the hope of further improvement, but which he is willing to exhibit at" 

 his house. 



A Podura-sli&e*, fortunately strongly protected with a thick glass 

 cover, having accidentally been subjected to so considerable a pressure as 

 to crush out the structure of a large scale, upon bringing it, by hap- 

 hazard, into the field of view with a magnifying-power of about 2000 dia- 

 meters, exhibited a structure indicated by the woodcuts here given, and 



Podura-scsble. 



drawn, in the presence of the writers, at Dr. Pigott's house by the accurate 

 artist Mr. Hollick, deaf and dumb and a rapid delineator without the 

 camera. Mr. Beaumont's surprise and admiration equalled that of Dr. 

 Pigott. This circumstance will excite no surprise when it is stated that 

 for four years the spherules of the Podura have been generally denied 

 and warmly disputed. In ordinary cases a crushed scale shows nothing ; 

 and as glasses are usually corrected to show the illusory spines or mark- 

 ings, these spherules are concealed. 



* Podura Lcgeeria vel domcstica. 



