30 



[Feb. 21, 



than to the quality and character of our photographic dry plates, or the 

 lack of skill of our experimenters, that we have to look for either cause or 

 failure. 



It will thus be seen that many new factors enter into the photographic 

 development of the new forces. Conditions seem to arise at every turn 

 that are entirely foreign to those encountered when we work with either 

 solar or artificial light, and this independent from the optical features 

 which I have mentioned. 



Now the question naturally presents itself as to which kind of sensitive 

 plate, or medium, should be used to obtain the maximum results of the 

 actinic action of the X rays, or in other words, by what means can we ob 

 tain the best permanent Photo-Sciographs? 



As to the difference between the action of the X rays upon gelatine and 

 collodion I would venture the theory that if these results are confirmed by 

 experiments here, that it is due to the fact that while gelatine arrests the 

 X rays, they pass through or penetrate the collodion film. It this should 

 prove to be the case, it would indicate the use of double-coated plates, or 

 of a stripping film upon a support impervious to the X rays, such as a 

 sheet of lead. By such means perhaps photographic results of still greater 

 value might be obtained. I will here state incidentally that the Schleus- 

 ner plate used in the German experiments is coated somewhat heavier 

 than the average American plate. 



I now come to another aspect of the possible development of the photo- 

 graphic properties of the new forces ; an experiment thus far untried in 

 .connection with the Rontgen rays. For this purpose I will turn back- 

 ward and take recourse to the original principles of heliography, and 

 suggest a series of experiments wherein we substitute for the gelatine dry 

 plate a highly polished sheet of metal, subjecting it to the action of the 

 X rays in the usual manner, and then seeking to develop the impinged 

 image, if there be one, with the fumes or vapor of mercury or iodine, or 

 the two in combination, a process well known to photo experts of the old 

 school . 



Tests should also be made upon the silvered copper plate coated with 

 the vapor of iodine and bromine and developed with the fumes cf mer- 

 cury (the old daguerreotype process) ; or upon plain sheets of polished 

 copper, silver or tin, and developed either with vapor, or by the applica- 

 tion of heat to the reverse side of the plate ; a process known as " Hunt's 

 Thermography." 



The above experiments are well worthy of a trial in connection with the 

 development of what may be called "photo-sciography." 



In conclusion I will call your attention to a curious coincidence. It 

 was in this room just fifty-three years ago during the centennial celebra- 

 tion of this Society (May 29, 1843) than an almost identical topic formed 

 the theme for discussion, viz.: Moser's theory of "Invisible photographic 

 rays," a theory which was then attracting great attention in scientific 

 circles on both sides of the Atlantic. Remarks upon the subject were 



