194 THE AMERICAN MONTHLY [Nov 



microscope be used. This augurs well for the populariza- 

 tion of the study of the higher aud more interesting do- 

 mains of microscopy, because an instrument can now be 

 constructed with a few cheap objectives capable of doing 

 better work than has hitherto been possible with objec- 

 tives costing twenty times as much. With a sixth-inch 

 objective in the first microscope and a one-half inch in 

 the second, I have resolved many markings and details 

 in well-known microscopic objects that could not be re- 

 solved with the best sixteenth-inch apochromatic of 

 high aperture. 



When higher objectives than a sixth and a half are 

 used the eye can no longer see the image, because of its 

 faintness. But where the eye fails, the sensitive plate 

 comes to our aid, and photographs the otherwise invisi- 

 ble image. The sensitive plate acts cumulatively and 

 gathers into one concrete result the continuous action of 

 the faint rays, for seconds and minutes of time, and thus 

 records the higher magnifications. 



A sixth on a sixth is probably the limit with an ordin- 

 arycamera in an ordinary dark-room, and with ordinary 

 photographic technique. Photomicrography has hitherto, 

 so far as I know, obtained no results much beyond 10,000 

 diameters or 100,000,000 times the area of the or- 

 iginal object. Any given detail in such a photomicro- 

 graph is made with the 1-100, 000, 000th the amount of light 

 that comes from the corresponding part of the object 

 observed. But I have succeeded in getting a picture 

 with only l-1300th of that amount of light. 



In the photomicrographic apparatus now being con- 

 structed, I have arranged to exclude from the interiors 

 of the microscopes and camera all dust particles and 

 aqueous vapor globules. Then the light can act cumu- 



lativelv hour after hour and dav after dav if necessarv, 



'' ' * " . . ' 



and the photogenic changes made on the sensitive plate 



will result wholly from the action of the image. From 



