146 



THE X-RAYS. 



plate placed iu tlie center of curvature, and at au angle of 45 degrees 

 with the axis. 



21. The X-rays proceed from the annode with this apparatus. As 1 

 have concluded from experiments with apparatus with various forms, 

 it is immaterial with regard to the intensity of the X-rays whether they 

 proceed from the annode or not. * * * 



WtJRZBURG, Physik. Institut d. Universitat, March 9, 1896. 



nr. — FURTHER OBSERVATIONS ON THE PROPERTIES OF X-RAYS 



(ABSTRACT). 1 



1. If between a discharge tube sending out intense X-rays^ and a 

 fluorescent screen one interposes an uutransmissible plate so placed 

 that it shades the whole screen, one can still observe a luminosity of 

 the barium platinum cyauite. This luminescence is still visible when 

 the screen is close up to the plate, and one is at first inclined to regard 

 the plate as transmissible. When, however, one 

 covers the fluorescent plate with a thick glass slide 

 the fluorescence becomes much weaker, and it com- 

 pletely disappears when instead of using the glass 

 plate one covers the screen with a lead cylinder 

 1 millimeter thick, which passes entirely over the 

 head of the observer and is closed by the uutrans- 

 missible plate. 



The phenomena described might be due to the 

 diffraction of rays of great wave length or to the 

 sending out of X-rays by the objects surrounding 

 the discharge tube, such, for example, as the air 

 ' '"' through which the rays pass. 



The latter explanation is the true one, as may be easily shown by the 

 use of the following apparatus. The figure shows a thick- walled glass 

 bell jar 20 centimeters high and 10 centimeters in diameter, which is 

 closed by a thick zinc plate inserted with cement. 



At a and h are lead shelves of the form of segments of a circle, each 

 of an area somewhat greater than half the cross section of thejar. At 

 the end of the glass jar is a zinc plate with a central opening covered 

 with a collodium film, and the two plates above mentioned prevent 

 X-rays which have passed through this opening from reaching the part 

 of thejar which lies above the lead plate h. Upon the upper side of 



1 Trauslation of a portion of the paper by Professor Ecintgen in the Sitzungsber. 

 der li. preuss. Akad. der Wissensch. zu Berlin, Jahrgang 1897, as reprinted iu Annalen 

 der Pbysili nnd Chemie, 64, p. 18, 1898. 



-All the discharge tabes mentioned in the following communication are constructed 

 according to the principle given under section 20 of my second communication. A 

 great part have been obtained from the firm of Greiuer & Friedricbs, in Stiitzerbach 

 1. Th., to whom I wish to express my thanks for the great quantity of material which 

 they have supplied to me without cost. 



