904 - 5 .] Mr T. Oliver on Diameters of Twisted Threads. 495 
one end of the thread, while the other consists of a notched lever 
on which a weight can be moved along to produce the required 
tension. The other end of the frame carries a sliding jaw, which 
can also be rotated by a handle, and the rotations indicated by 
a counter. Any length of thread from half an inch to four inches 
can be operated on, the sliding jaw being drawn back to any of 
the numbers on the base under the stage. The number of turns 
of twist is indicated by the counter when all the twist is taken 
out by turning the sliding jaw. The twist can also be varied at 
will by the same arrangement. The diameter of the thread is 
measured by means of an eye-piece micrometer, which is much 
better for this purpose than a stage micrometer, as with the latter 
it is impossible to bring the image of the widest part of the 
thread to coincide with the image of the scale if the thread is 
moderately thick. Another advantage of this instrument is that 
