of the sidereal universe, but in the fact that it marks out the stars affected by it as forming a subordinate system separated from other star-regions by starless spaces of enormous extent. Moreover the recognition of star-drift, especially if accompanied by spectroscopic evidence as to star structure, will probably become a potent means of ascertaining the architecture of various parts of the stellar universe. The other mistake resides in the supposition that at the present stage of the inquiry it would be desirable for me to examine and discuss those observations which promise to afford more complete information respecting the proper motions taking place within the star system. I can only deal with wide and general relations; and the charts of proper motions already constructed by me suffice for that purpose, since their construction has led to the general theory of star-drift which it was chiefly important to establish. Anyone who may have leisure for the work can now examine suitable star-catalogues for the recognition or correction of estimated proper motions, with the assurance that such work will reap a rich reward. But for my own part the task I have taken in hand is of another nature, and will permit of no expenditure of time on details, however interesting the subsidiary evidence which such details may afford. I wish rather to set others at work on the various parts of the wide subject of the constitution of the heavens than to enter myself on work of detail. The structure of the star-system as a whole, or at least of the portion within our scope, is the subject to which I address myself, and too minute a discussion of the subordinate details would impair rather than improve the general view which I desire to obtain. The proportions of a great structure are not javourably studied by approaching as near as possible to some particular part of it. Here my discussion of the subject of the constitution of the stellar heavens comes to a close so far as these pages are concerned. I take the opportunity of thanking students of astronomy, generally, for the patience and attention with which my views have been received. I trust and believe that those who have really examined the evidence I have adduced, will not have thought me dogmatic in the expression of opinions which I have based on a very thorough investigation of all the available evidence. I have been more than satisfied with the support I have already received. From Sir John Herschel in particular, who perhaps alone of all our leading astronomers, has taken special interest in the subject of the constitution of the heavens, I received encouraging expressions of opinion (which will one day be published), important not only in their relation to the researches I communicated to him, but in their prospective bearing on researches which have been completed since his lamented demise. For the rest, it is not to be expected, and, in fact, it is not possible, that general attention should be drawn to a subject so far removed from ordinary astronomical studies, whether practical, observational, mathematical, or theoretical. At all times in the history of Astronomy, the number of those who have been attracted to the study of the laws of stellar distribution has been small, though, strictly speaking, the very name Astronomy implies such study more specially than any other now recognised subject of astronomical research. But the true student of science is content if he fit audience find though few.' The investigation and demonstration of the truth are more important than the mere numerical array of supporters. Though, indeed, if on the one hand, as I had expected, few have been attracted to a subject of great difficulty, yet, on the other, I have had small occasion to complain of cavil or objection: and, if the results to which I have been led, or may be led hereafter, are just, it is a matter of indifference to me whether they be generally accepted at a late or early season, in my own lifetime or not till long afterwards. From the Monthly Notices of the Astronomical Society for October 1873. THE TRANSIT OF VENUS IN 1874. ON account of the important bearing of the transits of Venus upon the problem of the Sun's distance, men of science are looking anxiously forward to the two transits which occur in the present century. Although the later of the two will not take place for thirteen years, its circumstances have already been examined. Indeed both transits were subjected to examination by the Astronomer Royal so far back as 1857; and since then he has continued to put forward from time to time the considerations which have suggested themselves to him as his examination of the subject proceeded. Early in the inquiry he expressed the opinion that the method founded on the observed differences of the transit's duration, as seen from opposite points of the Earth's surface-which method had been the sole one employed in the treatment of the transit of 1769-is wholly inapplicable to the transit of 1874; and he suggested another method of utilising that transit,-a method less perfect in itself, more difficult (astronomically) to carry out, and involving processes of preparation essentially different from those which would be required under the other method. To the preparations thus called for, astronomers and geographers have hitherto, I believe, solely confined themselves. Having had occasion to examine the reasoning of the Astronomer Royal, and to test the conclusions he had arrived at, I have been led to form a totally different opinion of the value of the transit of 1874, so far as the simpler method of observation is concerned. I have found that, if consideration be made of internal contactsthe only phenomena on which estimates of the Sun's distance have ever been founded-the actual difference of duration which can be made available in 1874, is about 35m. or 36m., as against an outside value of 28m. in 1882, and an actual observed maximum of difference of 234m. in 1769. I am sensible that mere magnitude of observed difference is not |