Optical Curiosities of Literature. 225 



self as painfully surprised that the jury should have overlooked 

 this short and easy method, and so fallen into the mistake ; and is 

 the more anxious to call attention to it at once, as he finds that 

 unhappily the " mistake " has got copied into some microscopical 

 treatises. 



It would be hard to find now even a beginner who could read 

 this passage without smiling. No doubt we are more familiar with 

 these famous lines than observers were then ; but allowing for this, 

 and passing over any amount of contempt for the eyes of the jury, 

 it still seems unaccountable that to one familiar with scientific 

 methods, the possibility never suggested itself that the difi'erent 

 conditions of microscopical from ordinary vision might introduce 

 something which should modify the abstract calculation. But the 

 possibility, if it ever suggested itself, seemed so remote as not to 

 make it worth while even to take down the microscope to look. 



Practical errors, however, are not the only errors in this treatise. 

 There are others, which if less amusing are more discreditable, being 

 things of pure science. Take, for example, the passage in vol. viii., 

 where the author — perhaps someone else, and not Dr. Lardner him- 

 self — undertakes to show the ratioiiale of the magnifying property 

 of a simple lens. He premises the discussion by laying it down as 

 a thing of primary importance, and specially so because there is 

 " no subject on which more inexact and erroneous notions prevail." 

 Having sounded this flourish, he proceeds himself to explain it, and 

 explains it — wrong. An object brought nearer subtends a larger 

 angle, and the lens enables the eye to see it when brought nearer, 

 nearer than the customary ten inches ; — this is what the explana- 

 tion comes to. If the writer had ever happened to take out a pocket 

 lens while reading and held it before the book, he might have observed 

 that the print was magnified, although the distance remained the 

 same ; and might thus have been led to avoid the fate of himself 

 increasing the list of " inexact and erroneous notions." Some more 

 examples of the same kind may be found in vol. ix. 



Not to go farther away, a number of remarkable flowers might be 

 culled from the pages of the ' Monthly Microscopical Journal,' even at 

 this early period of its youth. One of them will be found in a paper 

 by Mr. Mayall on immersion objectives, in the number for February, 

 1869. Mr. M., who appears to have had an unusually extensive 

 acquaintance with glasses of this kind, observes, as it were in pass- 

 ing, that in consequence of the refractive power of water an immer- 

 sion glass never " has to do " with rays of greater obliquity than 

 48°. This observation, which is made with the easy air of feeling 

 perfectly at home in the subject, has evidently been a source of 

 much disquietude to readers of the article in after-times. Some 

 correspondents manifestly had become convinced that there must 

 be a mistake somewhere, though not able to say exactly where or 



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