THE AMERICAN 



MONTHLY 



MICROSCOPICAL JOURNAL. 



Vol. XII. FEBRUARY, 1891. No. 2. 



All communications for this Journal, whether relating to business or to editorial 

 matters, and all books, pamphlets, exchanges, etc., should be addressed to Ameri- 

 can Monthly Micf^oscopical Journal, Washington, D. C. 



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 TrUbner &^ Co., ^y Ltidgate Hill, Londoji, or to Mr. W. P. Collins, i^y Great 

 Portland street, London, accompajiied by the yearly p7'ice of five shillittgs. 



The Full Utilization of the Capacity of the Microscope. 



By EDWARD BAUSCH, 



ROCHESTER, N. Y. 



[Read at the American Society of Microscopists, Detroit, Mich., 1890.] 



[See Frontispiece.] 



The cover-glass may truly be called a necessary evil ; for, w^hile ab- 

 solutely required in microscopical investigations, there is no adjunct to 

 the microscope that has been and is productive of so much evil, and has 

 retarded the utilization of benefits made possible by the advance in the 

 construction of objectives so much as it. This fact was appreciated as 

 early as 1837, when the angular apertures were what would now be 

 considered extremely limited, and the appreciable effect of variations in 

 thickness of cover-glass was not then nearly so pronounced as it is at 

 the present time, even in modern objectives of a narrow angle. 



The accommodation for the different thickness was obtained by vary- 

 ing the distance between the systems of objectives, and has been followed 

 with modifications in the mode of obtaining the necessary motion up to 

 the present day. While open to some objection, it accomplishes the 

 purpose quite satisfactorily and must continue to be used until some- 

 thing better is suggested. 



One of the purposes of the homogeneous immersion is, as we know, 

 the avoida ce of the necessity of the cover-correction, in that the cover- 

 glass immersion fluid and front of objectives are to be one homogeneous 

 mass ; but evei;i under these conditions, which in practice were found to 

 be not constant, it has been found advisable to provide cover-correction 

 to obtain the highest possible results. However, even should this not 

 be found necessary in the development of improvements in this class of 

 objectives, it must be remembered that the majority of objectives will 

 always be dry, and especially so when such improvements, which we 

 hope are still to be made, are accomplished. It is an unfortunate cir- 

 cumstance that with this class of objectives the influence of variation in 



Copyright, 1891, by C. W. Smiley. 



