266 On the Navicula Spencerii. 



ever made to them in print, I mentioned their superiority to any 

 European glasses which I had seen, and I only claimed for Spen- 

 cer that, judging from memory alone, his lenses showed me all 

 that I had previously been able to see on the Navicula Hippo- 

 campus by the best English achromatic combinations. I made 

 this statement at the very time when I knew that some of the 

 best English microscopes in the country had failed in the hands 

 of their owners, to resolve the N. Spencerii which Spencer has 

 mastered ; and I did not claim superiority for Spencer's lenses, 

 as £ fully believed that these British microscopes would also 

 easily resolve the lines in question, if the peculiar management 

 of light which they require was once hit upon. The correct- 

 ness of this belief was shown by the first trials which I made 

 with two London microscopes, one made by Ross and the other 

 by Powell, and which was brought to West Point by their own- 

 ers for the express purpose of trying them upon the N. Spencerii, 

 an object which had hitherto baffled their endeavors to resolve it. 

 It was prior to these trials that the letter sent to London "early 

 in the year" was written, in which I stated that the English 

 instruments in the country had failed to resolve the new test, 

 and I feel very confident that in making this statement, I men- 

 tioned that up to that time I had not tried the English lenses 

 on this object myself, and also stated the belief I always en- 

 tertained, that they would resolve it by the aid of proper illu- 

 mination. 



It was certainly not so late in the year as the publication of 

 Mr. duekett's volume, when I informed the London artists through 

 Mr. Marshall, that by aid of their instruments I had satisfactorily 

 resolved both the longitudinal and transverse lines upon the ob- 

 ject, on the first occasion when I had an opportunity of trying 

 their lenses upon it. As I feel sure that the leading London ar- 

 tists will acquit me of all intention to underrate them, I will pass 

 from this subject to the easy task of showing that I had not over- 

 rated Spencers merits, nor the difficulty of the test object which 

 bears his name and which he first resolved. Upon these points 



I will cite from original documents. Let us see whether the 



Londoners did not find their best instruments apparently incapa- 

 ble of mastering the object which our American back-woodsman 

 had so successfully managed. The first letter which I received 

 from London, informing me of the reception of mounted speci- 

 mens of the N. Spencerii which I sent over to my friends in Lon- 

 don, is dated May 20, 1848, and contains the following remark 

 in which I have italicised the acknowledgments so frankly and 

 honorably made. 



"The evening I received your package there happened to be 

 a small gathering of our microscopic friends. Your slide with 

 the Navicula Spencerii underwent a long examination. We how- 



