A Recording Polarimeter

A recording polarimeter has been constructed. The principle of operation is essentially the replacement of an operator in conventional visual polarimetry by a photoelectric servo system. A photo‐multiplier tube is used which, in conjunction with a mechanical chopping system, delivers an alternating current signal proportional to the unbalance. The latter is filtered and amplified and actuates a servo mechanism. The precision of the system is ±0.005° for static balance and the speed about 0.5° per minute. Hence the arrangement compares favorably with ordinary visual operation. The construction of the instrument is discussed briefly and its performance is illustrated by examples.