628 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



the needed thickness of 1 mm. N.B. — If it is desired, with the same 

 combination as fig. 3", to work with uncovered objects, and not objects 

 under glass, it is sufficient to separate No. 1 by two turns of the screw 

 from No. 2. 



" If No. 1 is removed and the other two are left, as in Fig. 4", the 



Fig. 154. 



magnification is lessened, but there is an increase of focal distance, 

 whereby bodies of larger size, and even opaque ones, can be observed, 

 and it matters not whether they be covered with glass or mica, or be 

 uncovered. 



" The three objectives marked 6, 5, 4, as in fig. 2 a , are the series of 



