PAPERS READ IN SECTION A. 



1.— ACTION OF THE LATEX OF EUPHORBIA PEPLUS ON THE 

 PHOTOGRAPHIC PLATE. 



By H. G. CHAPMAN, M.U., B.S., r.nd J. M. PETRIE, D.Sc, F.I.C. 



Abstract. 



The milky juice or latex of this plant has been employed by 

 surgeons for the treatment of rodent ulcer. It has occurred to us 

 to test whether the dried latex has any action on a photographic 

 plate. A thin layer of the juice is spread on glass and is dried. A 

 photographic plate is placed a Uttle distance above the dried film. 

 When the plate is developed after three to seven days an image of 

 the film appears on the plate. If a word be written with the juice 

 a well defined photograph of the word appears on the plate. Such 

 an image appears when the distance between the film and the plate 

 is not more than one centimetre. The thicker the film of dried 

 juice the more dense is the image on the photographic plate. If 

 tissue paper, thick paper, thin aluminium foil, or gold leaf be 

 placed between the photographic plate and the film the image is 

 produced in the same way and is sharply defined. If glass or mica 

 be interposed the photographic plate is protected and no image 

 appears. We have been unable to obtain glass or mica less than 

 1-lOOth mm. in thickness. 



The film of latex may be heated to 200 C. without any diminu- 

 tion of its action on the photographic plate. At this temperature 

 it commences to char and the action on the photographic plate 

 remains powerful despite the destruction of the organic matter. 

 When the ash becomes white the action on the photographic plate 

 is much lessened. The photographic effect is also obtained during 

 the passage of a dry air or of carbon dioxide, also under greatly 

 reduced pressure. 



2.— lONISATION BY IMPACT. 



By PROFESSOR KERR GRANT, M.A. 



Abstract. 



The violent impact of one solid upon another is found to cause 

 considerable ionisation in the air in the neighbourhood. Experi- 

 ments in which a leaden bullet was fired at a target lead to the 

 following qualitative results: — 



1. A definite number of ions are produced when a leaden 

 bullet of given mass strikes an iron target with given 

 velocity. 



