106 Scientific Proceedings, Royal Dublin Society. 
tube, the side furthest from the wall, is now studded with minute 
erystals, which sparkle with the brilliancy of cut diamonds. 
The crystals could not be properly examined without removing 
them from the tube; and J do not care to interrupt the experiment 
at this stage. They are apparently rhombic; but they exhibit 
greater complexity than erystals deposited from sulphur solutions. 
The accompanying reproductions from photographs (figs. 1 and 2) 
give some idea of what the crystals are like. The photographs 
were taken under a magnification of fifty diameters. Owing to 
the cylindrical form of the tube, and to the fact that the crystals 
can only be seen in good definition from the side attached to the 
glass, it was difficult to photograph them properly. 
The largest crystals are not more than 0-2 mm. in length; and 
this is the growth of twenty-five years. The temperature has of 
course varied with the change of seasons; but the temperature of 
Dublin is very equable ; and it is improbable that the tube has ever 
been at a lower temperature than 0° C. or at a higher temperature 
than 22°C. Had the tube been fixed to the wall throughout the 
whole period, I expect the crystals would have become visible at an 
earlier date; because uniformity in the position of the tube with 
regard to surrounding objects would tend to localize the differences 
of temperature which cause the sublimate to settle upon certain 
parts of the tube. This condition has been observed for the past 
five years; and during that time the increase in the number of 
crystals has been very marked. ‘I'he increase in the size of some 
erystals is also very marked; but the size and form of a crystal 
are well known to have an important influence upon its rate of 
growth. 
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