368 HOW TO SEE WITH THE MICROSCOPE. 



A FEW WORDS CONCERNING THE PERFORMANCE OF OBJEC- 

 TIVES. 



Ed. Am. Jour. Microscopy Referring to the letters of Mr. E. 

 Gundlach, printed in the August issue of the Cincinnati Medi- 

 cal Mews, it was noticed that Mr. Gundlach bases his optical 

 laws on the performance of his own objectives, or at least he 

 appeals confidently to his objectives to sustain his positions, as 

 to working distance, resolution and angular aperture. 



Mr. Gundlach certainly has the right to state the principles 

 which govern him in the construction of object-glasses, and it 

 would be well if other makers would follow his example. But 

 his readers must keep constantly in mind that while the general 

 principles he sets forth may not, as a rule, differ materially from 

 those actuating other opticans, each and every one has a 

 handling characteristically his OMM, and that a necessary result 

 of his will be recognized in the characteristic, performance of 

 various so-called first-class objectives ; and further, that between 

 the extremes comprised in the ' v handling" above named, a large 

 margin obtains, sufficient to warrant the acceptance of one ob- 

 jective to the exclusion of another. 



The potency of these considerations is enhanced when we 

 remember that the slightest superiority in an objective is of the 

 highest importance. Beale says (*' How to Work with the 

 Microscope," p. 285) "It is certain that the slightest advantage 

 in defining power ought not to be underrated. * * * Im- 

 provement in the means of observation' is of the utmost im- 

 portance, and however slight, always leads to the discovery of 

 new facts." 



Again Dr. Beale writes (p. 283) ' The best object-glasses will 

 define clearly and accurately bodies which, from their trans- 

 parency, .are quite invisible under objectives only slightly in- 

 ferior to the first." 



It therefore becomes apparent that these little differences, 

 perhaps due to " handling" on the part of the optician, while 

 they are invaluable to the working microscopist, may also be 

 referable to the genius of the optician to a particular method 

 of "handling" known optical laws. 



