Some years ago, when employed in work that involved the use of a polarimeter. there was brought forcibly to my notice the great loss of time which the frequent reading of the Nicol dial necessitates. To avoid this, I had a special form of camera made for the purpose of recording the readings automatically. This method proved successful from the first, but it is only lately that the mechanism of the camera attained its final form; for it has required several years of experiment and alteration to evolve a form of camera which should be wholly automatic and yet reasonably simple. It will be readily understood that the function of the camera is to make a series of photographs of the scale-and-vernier of the polarimeter or other instrument, which, on subsequent examination, will show the relative position of the scale-and-vernier at the time of each exposure.