214 Trans. Acad. Sci. of St. Louis. 



getting very satisfactory results with four minutes of expo- 

 sure and a No. 8 stop. It seems very probable that by vary- 

 ing the proportions of this transforming solution, and perhaps 

 varying the oxidizing agents themselves, such exposures as are 

 now given in the negative process, may yield good positives. 

 The field open for experimentation along these lines is very 

 wide. The degree of illumination while in the transforming 

 solution, and the time interval for the transforming process, 

 are involved. The desirability of perfecting these processes 

 at the earliest possible moment, leads the writer to urge 

 those who have had wider experience in photography to lend 

 a hand in this work. If fine details can be secured in a posi- 

 tive with a camera exposuie such as is now required for a 

 negative, then certainly there is great reason to hope that by 

 exposing a plate during the whole time of totality in the long 

 eclipses which will shortly take place, we may hope to secure 

 better results than the present methods can give. In posi- 

 tive photography there can be no over exposure. In nega- 

 tive photography, over exposure is an approach to a zero 

 condition. In positive photography the zero condition has 

 been passed. 



Issued October 24, 1900. 



