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and the Use of the Kinematograph, 
This glass disc, when ready for use, is put into a light-prool 
box, and by means of a handle at the side can be spirally 
rotated, so that every part of it is in turn exposed before 
the small oblong opening in front of the lens. In ordinary 
kinematograph work the handle is rotated at a uniform speed, 
and a series of snapshots are produced, but for the work now 
required it is necessary to take time exposures, as the light in 
a greenhouse would seldom, if ever, be good enough for 
instantaneous photography, and also, if it were possible, the 
number of photographs thus obtained would be unnecessarily 
large ; as a large number are only required when rapid move- 
ment, such as that made by the stamens when touched or 
when a bud is opening, is taking place. For many parts 
of the day a photograph taken every quarter of an hour 
is sufficient. 
The practical difficulties were very great ; the principal 
ones were : 
(1) To obtain absolute rigidity of the apparatus. 
(2) Uniform exposure for each photograph, as photographs 
had to be taken at all times of the day and night and in 
all weathers. 
(3) The difficulty of having some one always watching the 
plant. 
(4) Compensating accurately for the growth in length of 
the inflorescence, so that the part of interest is always in 
the field. 
The first difficulty was removed by the construction of 
a heavy metal tripod stand. 
The second was soon removed by the use of an accurate 
actinometer, which must, however, be used for almost every 
photograph to ensure perfect results. The night photographs 
can be taken by means of a magnesium wire, accurately 
measured in lengths, or better still, by those who have electric 
light installed, with an arc light. 
For the third difficulty I am afraid there is no solution 
but the adoption of an elaborate and costly automatic 
mechanism. This has been done by Professor Pfeffer. 
