_Ascertaining Positions._—No observer should be without the means of determining exact positions. A ring-micrometer and comprehensive star-catalogues are most important accessories of the amateur. When a suspicious object is found its precise position should be instantly measured; but if no micrometer is at hand, the observer should carefully note the place relatively to adjoining stars, and then, after a short interval, re-observe it for traces of motion. In these comparisons the low-power eyepiece should be exchanged for one of greater amplification, because this will render a slight motion more readily sensible. If the suspicious object proves to be a comet, the extent and direction of its daily motion should be computed from the change in the observed places, and the information telegraphed to the Royal Observatory, Greenwich. A statement should also be given as to the diameter and brightness of the object; we may then be satisfied that it will be readily picked up at some of the many stations where prompt attention is given to this class of observation. Amateurs who do not attempt to obtain exact positions are sometimes condemned for their negligence in this respect, and most unjustly so. By far the hardest part of the work falls to them, and professional astronomers ought to be indebted to amateurs for leaving to their care an important feature of these observations. If the latter are to undertake the labour of measuring as well as discovering comets, then there will be nothing left in this line for the elaborate instruments of observatories to do. Yet, while thus objecting to amateurs, with their generally incomplete and inefficient appliances, being expected to perform the work both of discovery and exact observation, it cannot be denied that there is a great necessity for them to have the means of measurement, and to utilize them during the first few observations, which are usually made before the comet has been seen elsewhere, and will therefore possess great value if precise.