This consisted in
fixing two minute triangles of thin paper, about 1/20 inch in height, to
the two ends of the attached glass filament; and when their tips were
brought into a line so that they covered one another, dots were made as
before on the glass-plate. If we suppose the glass-plate to stand at a
distance of seven inches from the end of the shoot bearing the filament,
the dots when joined, will give nearly the same figure as if a filament
seven inches long, dipped in ink, had been fixed to the moving shoot, and
had inscribed its own course on the plate. The movement is thus
considerably magnified; for instance, if a shoot one inch in length were
bending, and the glass-plate stood at the distance of seven inches, the
movement would be magnified eight times. It would, however, have been very
difficult to have ascertained in each case how great a length of the shoot
was bending; and this is indispensable for ascertaining the degree to which
the movement is magnified.
After dots had been made on the glass-plates by either of the above
methods, they were copied on tracing paper and joined by ruled lines, with
arrows showing the direction of the movement.
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