1895-96.] Dr Macintyre on Rontgen X-Rays. 
145 
crossed we got a darker shadow still, it might only be due to the 
difference in thickness of the two layers. 
Second Observation . — One of the tourmalines was broken in two 
portions, and one of these was placed parallel with, and the other 
perpendicular to, the other tourmaline. Again, the dark square 
area was seen by direct vision. I could not say, however, that the 
density was greater than where the other portion of the broken 
tourmaline was lying parallel with the whole one. This rather 
suggested that the square dark area was caused by difference of 
density only. 
Third Observations . — These were made by photographs taken 
with different exposures. One with a single flash of the tube, due 
to one interruption of the coil ; others were taken with much 
longer exposures, and in all the same difficulties in distinguishing 
between the two conditions arose. In the first photograph a 
shadow of one tourmaline is seen, proving the absorption of some of 
the x-rays. In the second, of one whole tourmaline, and a portion 
of the other, a greater density is to be noted where two layers are 
lying parallel with each other than where only one tourmaline 
interferes with the rays. The third photograph shows the whole 
tourmaline covered at one part by a portion of the broken tourma- 
line lying parallel with its axis. The other broken tourmaline is 
placed at right angles, and the question arises whether the density 
of the square area is greater than where the two tourmalines are 
lying parallel with each other. The photographs bear out the 
observations by direct vision, and would appear to give negative 
results. 
VOL. XXI. 
3/10/96 
K 
