46. The slit and lens, together with the tube in which they are usually supported, are called a collimator.
"A Text-Book of Astronomy"
George C. Comstock
There is a well-marked annual periodical change in the position of the Transit Circle, the southerly movement of the eastern pivot having its minimum value in September, and its maximum in March, the extreme range being about 14 seconds; and there is a similar change, but of smaller amount, in the position of the collimator.
"Autobiography of Sir George Biddell Airy"
George Biddell Airy
The point then that had to be aimed at was to form two spectra from the same source of light, and with the same beam that passes through the slit of the collimator.
"Colour Measurement and Mixture"
W. de W. Abney