NEGATIVE MAKING 73 



The remaining proceedings are those already 

 detailed, the focusing being completed through 

 both screens. The length of bellows exten- 

 sion and double screens, have so lessened 

 brilliance of the acetylene flame that in con- 

 nection with the slow plate a somewhat long 

 exposure is manifestly necessary. Eight 

 minutes are accordingly given, the plate being 

 developed with eiko-hydro. Result, a fine 

 negative at +825. Shown in Fig. n. 



Another example of high power work, in 

 which the amplification is pushed closely to 

 practical limits with either of the radiants we 

 have been using, may probably be given with 

 profit to some of my audience. I have chosen 

 the well-known test diatom, Pleurosigma angu- 

 latum as the object and will endeavor to 

 photograph it, " while you wait," at 3,000 di- 

 ameters. We could obtain better results by 

 making the negative at 1,000 diameters and 

 enlarging from this, for it is a curious fact 

 that the best work on this diatom can be done 

 at about the latter magnification. But since 

 many have expressed a desire to see a negative 

 made direct at a great amplification we will 

 endeavor to gratify them. Really there is but 

 little difference between the requirements for 

 this and the preceding example. The optical 



