140 HOW TO SEE WITH THE MICROSCOPE. 



suffice to defeat the maximum performance of the bal- 

 sam apertures, and the higher the balsam angle, the 

 greater the " bother " attending their use. 



Nor is there anything so exceptional in all this. In 

 any instrument of precision, when, by successive im- 

 provements, we gain width of effective range, and, 

 simultaneously, a nearer approach to accuracy of deter- 

 mination, then, in ninety-five cases out of the hundred, 

 do we, in like manner, increase the complications of 

 the instrument; thus introducing " inconvenience " and 

 " bother," and, be it known, an accompanying call for 

 skilled manipulators. 



We often hear another remark to wit, that those 

 owning and using the class of objectives we are now 

 considering, do nothing else than " fight them." Before 

 attaching any definite force to this remark, it will be 

 well to inquire, " for what purpose is \he battle!" Is 

 it to determine which of two objectives, differing in 

 construction, but supposed to be nearly alike in per- 

 formance, is the better one, and with the purpose 

 (avowed or otherwise) of rendering some contribution 

 to a scientific end; or is it that "A" battles " B," the 

 object being on the part of " A" to assure himself that 

 his glasses are not behind the age in quality of per- 

 formance; or, again, may it be that " C," being re- 

 quested by his inexperienced friend "D" to select for 

 him an objective in every respect fully up to the times? 

 Or, to mention a very possible case, does "E,"who, 

 having a few hours of daily leisure, desires to appro- 

 priate the same to the study of object-glasses, with the 



