358 



SCIENCE. 



[N. S. Vol. III. No. 62. 



to some agent which had produced a photo- 

 graphic effect; althougli the sensitive plate was 

 completely in the dark within the printing 

 frame and thoroughly protected from light rays 

 as generally understood. Apparently, however, 

 the plate had been over-exposed, and it seemed 

 that better results might be obtained by shorter 

 exposures. Therefore other plates of the same 

 kind were exposed by us for gradually decreas- 

 ing periods, under negatives and positives, and 

 shields, respectively of aluminium, hard rubber, 

 black cardboard and double thicknesses of 

 opaque needle paper. 



Positives were obtained in each case resem- 

 bling those obtained by the photographer with 

 ordinary methods, in some cases the exposures 

 being as brief as ten minutes. 



Shadowgraphs (' skotographs,' or 'skia- 

 graphs ') were also produced by the method em- 

 ployed by Prof. Eontgen, except that the source 

 of energy was the direct sunlight in place of 

 the rays from a vacuum tube, i. e. , coins placed 

 upon the aluminium shield produced shadow 

 prints on the sensitive plate. 



It is obvious that these experiments prove 

 the presence in sunlight of the peculiar rays de- 

 scribed by Prof. Eontgen, or of others posses- 

 sing the same properties, namely, the power of 

 penetrating substances opaque to ordinary light 

 rays. 



Prof. Eontgen states, in the second clause of 

 his article (as translated and printed in Science 

 of February 14th, p. 227,) ' that some agent is 

 capable of penetrating black cardboard, which 

 is quite opaque to ultra-violet light, sunlight 

 or arc-light.' If this statement refers to svm- 

 light in toio, including the visible and invisible 

 rays, it is evidently contravened by our experi- 

 ments, which demonstrate beyond a doubt the 

 existence of an ' agent' in sunlight, which ac- 

 complishes the work of the ' X-rays. ' 



Prof Eontgen refers to the possibility that 

 the effect is due to a fluorescence produced in 

 the material of the sensitive plate. One of our 

 experiments seemed to point to the correctness 

 of this hypothesis. Fixed photographic prints 

 on albumin paper placed between the alumin- 

 ium shield and the sensitive plate gave cor- 

 responding negative effects ; but the space 

 covered by these prints was evidently more in- 



tensely acted upon by the rays than other parts 

 of the plate covered only by the aluminium. 

 Should fluorescence be produced by these rays 

 in silver emulsions, it would perhaps explain 

 the phenomena. Prof. Eontgen further states 

 that silver in ' thin' layers allows the rays to 

 pass ; but we have shown that some of the rays 

 are partially stopped by the exceedingly thin 

 film of silver in the ordinary photographic neg- 

 ative. 



It is obvious that the discovery of these rays 

 in sunlight opens up an entirely new field for 

 experiment and is of the highest practical im- 

 portance to all photographers. 



We hope to supplement this preliminary state- 

 ment by a presentation of the results of our at- 

 tempts to solve a number of interesting problems 

 that have been suggested. 



Chaeles S. Dollby, 

 Seneca Egbert. 



[Eesults somewhat similar to those given by 

 Drs. Dolley and Egbert have been announced 

 by M. Gustav Le Bon, Prof S. P. Thompson 

 and others. The conditions, are, however, so 

 complex that it is difiRcult to eliminate sources 

 of energy other than the Eontgen rays. Care- 

 ful experiments at Columbia College have not 

 detected any penetration of thin (j-J-j inch) 

 sheets of aluminium by sunlight, though ebonite 

 and wood of considerable thickness are pene- 

 trated by ordinary light. Ed] . 



EONTGEN EAYS FEOM THE ELECTRIC AEC. 



Prof. S. P. Thompson is reported * to have 

 discovered the Eontgen rays in the radiations 

 emitted by the electric arc, and to have suc- 

 ceeded in getting excellent shadow pictures 

 with them. The present writer had carried 

 out the following experiments before seeing the 

 report of S. P. Thompson's work, and had 

 reached conclusions opposite to those reported 

 of Prof Thompson. 



Very rapid (Carbutt's ' Eclipse 27 ') and me- 

 dium (Carbutt's ' Orthochromatic 23 ') plates, 

 placed in ordinary holders, were laid in deep 

 lead trays and masked with two to five thick- 

 nesses of black cardboard, including the card- 



* London, Electrician, January 24, 1896. Digest in 

 the Electrical World February 15th. 



