xviii Trans. Acad. Sci. of St. Louis. 



zanillo, making the ascent of Popocatepetl to the summit in 

 doing so. The address was illustrated by a large series of 

 lantern slides, presenting some of the more striking features 

 of the physiography and vegetation of the country, and illus- 

 trating the customs of the Mexicans. 



Messrs. John E. Conzelman, Otto Schrowang and W. H. 

 Thomson, Jr., of St. Louis, were elected to active member- 

 ship. 



Three persons were proposed for active membership. 



January 21, 1901. 



President Engler in the chair, twenty-seven persons present. 



The death of Mr. Charles P. Choutc^au, a charter member 

 of the Academy, and the resignation of Professor L. T. More, 

 were reported by the Council, 



Rev. M. S. Brennan read a short sketch of the progress of 

 astronomy in the United States, in which the material equip- 

 ment and discoveries made in that science in this country 

 during the past century were passed in review. 



A paper by Professor T. G. Poats, entitled Isogenic projec- 

 tion, was presented in abstract by Professor Nipher. 



Professor F. E. Nipher showed by means of the lantern a 

 series of negatives printed by contact from a lantern slide or 

 positive picture, by the light of a 300 candle incandescent 

 lamp. The unit of exposure adopted was one lamp-meter- 

 second. The exposures varied from 0.0054 to 4800. All 

 were developed in the dark-room with hydrochinon, those 

 above 0.1 exposure having in the bath one drop of saturated 

 hypo to the ounce of bath. The plate having an exposure 

 of 0.1 seemed to be normally exposed. An exposure 210 

 gave a negative showing some fogging, but a print from it by 

 ordinary methods gave a very satisfactory result. With longer 

 exposures, the plate began to reverse, locally. With an ex- 

 posure of 3600, which was an exposure of one hour at a dis- 

 tance of one meter from a 300 candle lamp, half of the plate 

 still showed as a negative. The shadow on the gown of a 

 figure in the landscape showed white as a negative, and the 



