in Pa | 
These broadenings, however, are exactly ofa character as is to he expected 
in the case of diffraction; and therefore as long as another explanation 
is wanting, we can but consider our three plates as so many proofs 
of diffraction of the Röntgen-rays. 
Of the most important parts of N°. 1, 4, B and C we have made 
enlarged copies on glass by means of the microplanar, on which, if not so 
clearly as under the microscope, the broadening of the image of the slit 
is yet verydistinct; the difficulty of reproducing these enlargements well 
has made us refrain from publishing them; we are quite willing to 
send these copies to those who are interested in them. 
As to the question to estimate the wave-lengths of these rays, 
various ways are open; but in no case can one attain at anything 
but a very rough estimation, as on one hand the real nature of the 
kind of radiation dealt with is unknown, so that it is uncertain 
with which kind of diffraction-image our images must be compared, 
and on the other hand it is very difficult to find out what is accur- 
ately the physical meaning of the limits of the image, on which is 
pointed when measuring. | 
If however we are forced to limit ourselves to a very rough esti- 
mation it is rather indifferent, as far as the result goes, which 
of the ways already indicated*) we take; the simplest method 
deserves recommendation, namely the one we followed in our first 
communication about this subject, based upon our estimating the 
tabular width v of the slit equal to 1.3 at the place where the 
broadening begins to make its appearance in the image. With a radiation 
of simple periodical disturbances this tabular width is connected with the 
wavelength and the linear width, and with the known distances 
a and 6 by means of the relation : 
2 (a+b) 8° 2 (a+d) 
UZ Oe - - 8 
ab 2 tie? ab 
As in the experiments « and 6 both amounted to 75 em. we 
obtain after substitution of the value of +, 
A ONE Ee 
From the above table ensues for s: the width of the slit where 
En deed 
‘ 
for the plates A, B and C. From this would ensue for the 
the broadening begins to appear, respectively about 7 
1) H. Hac and C. H. Wino. These reports 7 page 200, 1899. CG. H. Winn 
Wied. Ann. 68, page 896 and 69, page 327, 1809; Physik. Zeitschrift 2. p. 189, 
265 and 292, 1901. A. Sommerrenp, Physik. Zeitschrift 1, pg. 105, 1900 and 2, 
pg. 58, 1900; Zeitschrift. f. Math. und Physik. 46, pg. 11, 1901, 
ta 
~ 
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