"* [Feb. 21, 



plates. I knew that several of them gave off a great deal of fluorescence. 

 I have only produced plates printed on glass ; but I shall take up a line 

 of experiments at once by producing some on thin celluloid ; because, 

 for the physician and others that have cases to tend where the flat plate 

 would be very diSicult to use, the celluloid can be enclosed in an envelope 

 — sufficiently opaque to ordinary light — and can be bound around the 

 elbow or the shoulder or any part sufficiently round where a plate would 

 have to lie flat ; and I think it would find in that case several uses. I 

 have been experimenting with some professors (which matter I am not at 

 liberty just now to mention) when I made a sciograph negative of a 

 woman's hand in twenty minutes, plates as large as 14 x 17 being used. 

 A film of the same size could be bound around the back, for instance ; 

 and I think in that way that possibly the celluloid film (it is ^^g-ths 

 thick) may possibly come in use. As it has been mentioned that Mr. 

 Edison has been using slow to quick plates, I have not as yet experi- 

 mented with anything slower than a very rapid plate and am inclined 

 to increase its sensibility ; and I think that in a measure I have succeeded, 

 as Prof. Goodspeed has shown you. Since the sensibility of these rays is 

 a subject that requires both study and experiment, I do not propose at the 

 present moment to say that I fully understand all of its requirements ; 

 and it is in its experimental stage. I shall not let the matter drop ; I find 

 it very difficult to find any tubes that are giving the proper X rays. The 

 one that Prof. Goodspeed is using, so far as I have seen, is the best one 

 that I have come across. I have been using one to-day with which I gave a 

 full half-hour's exposure and got no results. The reason was explained 

 to me to-night in the remarks that were made that when a blue or a 

 purple color comes from the negative or cathode end of the Crookes tube it 

 is not efficient in giving off" the X rays. There is no doubt that a great 

 many professors who are trying these experiments and getting negative 

 results are working with inefficient Crookes tubes. 



Eemarks of Dr. William Pepper were as follows : 



I rise only to occupy the attention of the Society for a single moment. 

 In pursuance of the suggestion of Dr. Minis Hays to me, we owe very 

 much of the pleasure of this evening's discussion, he having suggested 

 that I write to some friends in Canada ; and as a result of it, I present 

 from Prof. Cox, of the MacDonald Physics Building at McGill Univer- 

 sity, Montreal, this brief note, accompanied by these four verj'- excellent 

 photographs illustrating the application of this method to surgical 

 diagnosis. 



" The MacDonald Physics Building, 

 "McGiLL University, 



"Montreal, February 18, 1896. 



"Dear Sir : — Dr. Shepherd has sent tome your letter expressing a wish 

 to have some of our photographs for the meeting of the American Philo- 

 sophical Society on the 21st. 



