and is defined without any ambiguity, such as is contemplated on p. 348. Of course, if we take a broad belt of sun-spots instead of an infinitesimal one, A will be slightly different from the given value. In the extreme case, when the whole sphere is all over covered with spots, the mean foreshortening factor will be (Disc) - 1⁄2, and λ( = λ) = 30°. The variation of λ being so (Hemisphere) slight, we can practically put = 30° for all cases. 2°. The brightness at maximum being from 40 to 100 times that at minimum, it seems very probable that at maximum the whole surface of the star is in activity and covered with faculæ. This may be confirmed by what we know of the "polar type" of the Sun's corona at maximum, when the streamers, are numerous in nearly all solar latitudes (M.N., lxiii. p. 482), in opposition to the "equatorial" or "wind vane type " at minimum. In this hypothesis the maxima of polar and "equatorial view" must coincide, and this would seem a new argument for the more preferable "hypothesis of superposing maxima." If these remarks are right, it follows that the latitudes given on page 348 for λ= 30° are the most probable. Now, starting from the equation B=8F, we can calculate F. Subtracting the numbers of Table III. Group I. (the “polar view group") from unity, and multiplying by 1.6, we get log F 160 139 '99 '63 '21 '00 '10 48 96 112 1*33 1'44 log sin λ=9'70 9'62 945 9'28 9′13 9°19 9°52 9'91 9'99 *00 9'99 9'93 log F F 22 =190 177 154 135 108 081 0'58 0.57 0.97 1'12 134 1'51 13 22 32 82° 78° 58° The hypothetical law suggested by these numerical results can hardly be better expressed than in the words used by the Astronomer Royal for characterising the sun-spot phenomena from 1874 to 1902 (M.N., lxiii. pp. 452–3). We have only to omit the words between brackets :- "The years of maximum showed spots in practically every latitude [between 30° N and 30° S]. In the years following the maximum a marked tendency was shown for the spots to appear in lower latitudes. . . . about one or two years before minimum no spots were seen outside the limit of 18° from the equator. But immediately minimum was reached the spots became more widely extended in latitude, owing to the occurrence of outbreaks in high latitudes. Thus at minimum each hemisphere, considered separately, showed two clearly defined spot-zones marked off from each other by a broad belt in which there were no spots at all. Of these two spot-zones in each hemisphere, the lower appears to correspond to the series of spots of the expiring cycle. During the periods of increase the equatorial belt was almost wholly free from spots, indicating possibly the complete disappearance of the last members of the old cycle. At maximum, however, the spots of the new cycle were most widely spread, and were even seen in the near neighbourhood of the equator ... Finally, I wish to tender you my sincere congratulations on your original interpretation of the long-period variation, and to express the hope that my little remarks may contribute to enhance its evident plausibility. It goes without saying, that you may dispose of these remarks at your own pleasure.-I am, very faithfully yours, J. STEIN, S.J. Measures of Southern Double Stars in 1907. By James L. Scott. The following measures of southern double stars were made with the same 5-in. refractor as those in M.N., vol. lxiv. p. 52, bright wire illumination being used throughout. The weather during 1907 was, on the whole, distinctly poor, cloudy nights and bad definition. being the rule rather than the exception; the number of stars measured was therefore smaller than usual. Note on the adopted co-ordinates of the Bombay (Colaba) It may be desirable to point out that the relatively large change in the position of the Colaba Observatory, as given in the Nautical Almanac for 1909 and following years, from that given in the Nautical Almanac for 1896-1908 inclusive, arises from the large difference existing in that part of India between the geodetic and astronomical co-ordinates. I am indebted to the courtesy of the Headquarters Staff of the Trigonometrical Branch of the Survey of India for the following particulars as to the position of the Colaba Observatory: Latitude, Astronomical. Geodetic. It will thus be seen that the quantities given in the Nautical Almanac for 1909 and onwards are the astronomical latitude and the geodetic longitude. On the other hand, up to and including the current year, the quantities given are the geodetic latitude and the astronomical longitude; the values of these co-ordinates given above being later, and presumably more accurate, than those communicated to me in 1892, and which appear in the Nautical Almanac for the years specified. |
