_van Maanen’s star._ Another very faint star, which has the high surface-temperature of 7000 degrees. Notwithstanding this, it only emits ¹/₆₀₀₀th of the sun’s light. Consequently its diameter is only about ¹/₁₁₀th of the sun’s, the star being if anything smaller than the earth. Its weight is unknown, but its substance is in all probability packed even more closely than in Sirius _B_. The discussion of this sample of stars suggests that the majority of stars in space are smaller, cooler and fainter than the sun. Stars exist which are far brighter than the sun, but they are exceptional, the average star in the sky being a small dull dim affair in comparison with our sun. With this sample of the average population of the sky before us, we may proceed to discuss the various characteristics of stars in a systematic way, without fearing to mention extremes. Let us begin with their weights. STELLAR WEIGHTS. The two stars of smallest known weight in the whole sky are the faint constituent of Kruger 60, just discussed, and the faintest constituent of the triple system ο₂ Eridani, each of which has a fifth of the sun’s weight. But the stars whose weights are known are so few that there can be no justification for supposing these to be the smallest weights which occur in the whole universe of stars. A general survey of the situation, on lines to be indicated later (p. 281), suggests that there may be many stars of still smaller weight, but that very few are likely to have weights which are enormously smaller. Probably very few stars weigh as little as a tenth of the sun’s weight. The vast majority of stars have weights intermediate between this and ten times the sun’s weight. Stars which weigh even three times as much as the sun are rare, those which weigh ten times as much are very rare, probably only about one star in 100,000 having ten times the weight of the sun. Even higher weights undoubtedly occur—we have already mentioned Plaskett’s star, whose two constituents have more than 75 and 63 times the sun’s weight respectively, and the quadruple system 27 Canis Majoris which to all appearances weighs 940 times as much as the sun—but such instances are very, very unusual. We may say that as a general rule the weights of the stars lie within the range of from a tenth to ten times the sun’s weight, and we shall find that stars differ less in their weights than in most of their other physical characteristics.