300 HOW TO SEE WITH THE MICROSCOPE. 



London controversy of the Messrs. Piggott and Wen- 

 ham on the podura question, and also gave the state- 

 ments of other English observers. Among the illustra- 

 tions accompanying this article were five or six cute 

 showing the same scale of Podura as seen in the micro- 



O 



scope under different illuminations. Thus one identical 

 scale was exhibited to the reader as widely changed in 

 its aspects as could have occurred had dissimilar scales 

 been selected for the comparison. One or two of the 

 results shown were evidently owing to distortion occur- 

 ring from the use of a badly corrected objective. 



Now let it be remembered that Mr. Michells, in thus 

 stating his authority for the wwkhiterpretations of the 

 microscope, worked with legitimate material, and the 

 work over the podura presented was such as had been 

 arrived at by English microscopists of acknowledged 

 competency. There must be something wrong ; in what 

 direction shall we look for the cause thereof? 



So far as the exhibition of " the markings " of the 

 podura are concerned, they are an easy test ; i. e.< almost 

 any common-place glass will show them after a fashion, 

 while what would be known as a " real honest working 

 sixth or eighth " will show these markings with consid- 

 erable force; and such a display would likely be as 

 acceptable to the novice (or to those who had never 

 worked with better objectives), as the view given by a 

 superb high balsam angled glass by Spencer or Tolles. 

 But mark this: Hardly two of the " real honest work- 

 ing glasses," owing to the hap-hazard character of their 

 corrections, will give the same appearances, while the 



