( 248 )- 
to be what was to be expected with rectilinear propagation but 
presented broadenings from which an estimation could be derived 
concerning the value of the wave-length which proved to be of the 
order of 0,1 u u. 
In September of last year in one of the meetings of the “Deutsche 
Naturforscher Versammlung” at Hamburg Dr.W arrer') protested against 
those experiments; he had arranged his experiments in entirely the 
same way as we had; moreover he had taken still greater precautions 
to get a steady mounting of the slits and the photographic plate and 
he had used stronger Röntgen-rays. WaLrer obtained images quite 
similar to the second slit and attributed our broadenings to inac- 
curacies of the photografic plate brought about by long development. 
These negative results gave rise to a renewed investigation on our 
side, now that we had greater means at our service than three years 
ago. We have succeeded in obtaining more clearly than before 
phenomena of diffraction, so that according to us one can no more 
doubt the character of Réntgen-rays to be that of disturbances in 
the ether. 
The method of investigation has not changed in principle, but 
making use of the experience obtained by Dr. Warrrr and ourselves 
we have been able to make improvements still in some respects. 
On the upper surface width 5.5 em. of an iron beam of I-shaped 
profile, long 2m. and high 12.5 em. three pieces of angle-iron were 
screwed down, one at the end, the two others 75 em. and 150 cm. 
distant from it, the edge perpendicular on the length of the beam and 
the side of 3.5 em. erect; in the figure the two first pieces of angle- 
iron are visible; against the vertical sides brass plates — 12 em. 
high, 10 em. wide and 4 mm. thick — were screwed. In the 
middle of plate I was the first slit, in the middle of plate II the 
wedge-shaped diffraction slit while against the third plate in a 
black envelope the photographic plate was clamped’). During the 
experiments the second and the third of these brass plates were enclosed 
in an oblong leaden case, which had to prevent the secondary 
Öntgen-rays or rays diffused by the air, from affecting the photo- 
graphie plate and causing a fog. 
The iron beam was fastened by means of plaster of Paris on 
two free-stone plates borne by free-stone columns ; the columns were 
placed on a firm pillar; on this same pillar, likewise on a free-stone 
plate borne by a stone column, was the Réntgen-tube in a large leaden 
1) B. Warrer, Physik. Zeitschrift 3. p. 137, 1902. 
*) Scuteussner’s “Röntgenplatten” were used. 
