A new dark-field micrometer for double-star measurement

It remains a fact that some of the grandest achievements of science are due to workers who have had to be content with very simple and perhaps roughly constructed apparatus, the outcome of their own ingenuity, called forth by the necessities of the case. The writer claims the applicability of the foregoing remarks to his own case only so far as they relate to the necessity of trusting mainly to his own resources in his very limited field of scientific work.
The instrument of which the following is a description, has been in this way the outcome of his necessity. Its special function is the measurement of very minute angular distances, such as those of double stars, giving at the same time the angle of position with reference to the meridian.
A few preliminary remarks on some of the existing forms of Micrometer may help to elucidate the special adaptability of the instrument to be described for the work for which it was designed.