As to star-colours, it must be admitted that our knowledge is in an unsatisfactory condition. The results of past observation show discordances which are difficult to account for. When, however, all the circumstances are considered, we need feel no surprise at this want of unanimity. In certain cases it is probable that actual and periodical changes occur in the colours of stars, though absolute proof is still required. Atmospheric variations unquestionably affect the tints of stars, and some alterations depend upon altitude, for a celestial object seen through the dense lower air-strata near the horizon will hardly preserve the same apparent hues when on the meridian. Telescopes are also liable to induce false impressions of colour, and especially by the employment of different eyepieces not equally achromatic. And the observer’s judgment is sometimes at fault through physiological influences, or he may have a systematic preference for certain hues which little impress another observer. Those engaged in this branch feel the want of a reliable and ready means of comparison, and several have been tried; but there are objections to their use, and it seems that the best objects are furnished by the stars themselves. Let the observer study the colours of well-known stars, and familiarize his eye with the distinctions in various cases (also with the differences due to meteorological effects &c.); he will then gradually acquire confidence, and may use these objects as standards. The difficulty will be that they cannot be directly compared, in the same field, with other stars; but relative differences may be noted by turning the telescope from one object to the other. This will be better than forming estimates on the basis of an artificial method, which will sure to be troublesome to arrange, and probably erroneous in practice. In some stars the colour is so curious as to be attributed with difficulty, and with regard to faint stars colour-estimates are often unreliable; so that it is not desirable to go below the 9th mag. unless a very large instrument is employed. The necessity of being constantly on the look-out for temporary stars has been already mentioned. There is also the need for further observations of such of these objects as still exist. They are, however, very minute, and the observer will have to be careful as to their identity. Though no great revival in brilliancy is to be expected, these objects exhibited some singular fluctuations during their decline, and it is important to keep them under view as long as possible.