WORK OVER DRY MOUNTS, ETC. 299 



defining powers, always choose a balsam mount, and the 

 thinner and weaker the shells (within reasonable limits) 

 the better and the more palpable will be the comparisons. 



We advise every lover of a good objective to provide 

 himself with a slide of the genuine English podura, as 

 a matter of course dry mounted, and let him be careful 

 to keep it dry! Amount that has once, only, been 

 swamped in water will be probably badly damaged ; and 

 should it occur that water leaks through the cement, it 

 should be immediately dried by moderate artificial heat, 

 and subsequently laid away in a warm place for several 

 hours. Too much care cannot be taken with a really 

 valuable slide of podura. Prof. Phin says, in his excel- 

 lent work, " How to Use the Microscope," alluding to 

 the podura scale, " page after page has been written for 

 the purpose of showing how the podura ought to look* 

 and still the question seems to be undecided." 



A year or two ago a lively discussion sprang up in the 

 London Monthly Journal of Microscopy , between Messrs. 

 Piggott and Wenham, the former contending that the 

 true resolution of the podura resulted in dots. Mr. 

 Wenham, on the contrary, warmly taking sides with 

 Ross and Beck, holding that the " exclamation points" 

 were the proper thing to be shown. A month or two 

 later a most curious article appeared in the *' Popular 

 Science Monthly" contributed by Mr. John Michells, and 

 entitled " The Microscope and its ^/^interpretations." 

 The point of Mr. Michell's article was to show the want 

 of reliability attending observations made with the mi- 

 croscope. To make this point salient, he referred to the 



