OBJECT GLASSES. 101 



viously accomplished and thereby astonishing the world, 

 sorely punching the English opticians (who flattered 

 themselves on secure ground at the head of the profes- 

 sion) with an exceedingly sharp stick; with this glass 

 Mr. Spencer succeeded in displaying both sets of lines 

 on the diatom, now known as Navicula Spencerii. 



The London makers followed suit, giving especial at- 

 tention to the extension of aperture, and, as might be 

 reasonably expected, the problem was to get light of 

 extreme obliquity somehow through the lens, nor were 

 they (the makers) very particular to stand on the order 

 of its going; hence it came about that very many 

 glasses were made and sold having increased angle, by 

 virtue of which they were able to display certain ac- 

 knowledged difficult tests ; but, on the other hand, the 

 lateral pencils being poorly corrected (if corrected at 

 all), these glasses could not compete by centrally dis- 

 posed light with the well-corrected but narrow angles 

 previously in use. 



It was, therefore, to the wide-angled glasses of that 

 day that Dr. Carpenter's remarks had force, the highest 

 possible angle attainable being then limited by popular 

 opinion to Ib5. What is now known and recognized 

 as a high-angled glass of 175 was then not only 

 unknown, but would have been deemed a sheer im- 

 possibility, and it therefore becomes obvious that any 

 remarks at the time referred to, whether by Dr. Car- 

 penter or by other authors, cannot be applied consist- 

 ently to the wide-angled glasses of the present date. 



Tliose were the days, too, when the resolution of the 



