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)DRESS. 



RY TRANSLUCENT 

 GNIFICATIONS. 



st, 1908.) 



diatoms at high magnifica- 

 ;er. In the first place, it is 

 between the object and the 

 often very difficult to show- 

 id crisply, especially when 

 hi, as is almost always the 

 3dingly minute, 

 irectly proportional to the 

 )f the mounting medium to 

 ring the refractive index of 

 Canada balsam as l - 52, the 

 arence has been somewhat 

 very small ; hence troubles 

 ,x by comparison, the differ - 

 improvement in the possi- 

 ; contrast effects are more 

 Substituting monobromide of naphthalin (1*658), 

 the differentiating power is again increased, whilst by employing 

 realgar the microscopist has a still greater accession of possi- 

 bilities. It is evident, then, that this arsenical compound is by 

 far the best medium in which to mount diatoms, and it is a 

 subject of regret that more diatom-mounters do not take advan- 

 tage of its high index of refraction notwithstanding the many 

 difficulties attending its use. The photomicrographer, however, 

 should always recollect, if he has a special diatom to photograph, 

 to do his best to obtain it mounted in this medium, as it is 

 far easier to get good results than if it is mounted in any other. 

 Unfortunately, however, it frequently happens that one is unable 

 to obtain a realgar mount of some rare species, or to remount 

 a particularly fine specimen which is already put up in some 



pronounced. 



