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THE SUN.

It may be interesting to notice that a similar method ofobservation has also been applied to some of the minor planets.Even when nearest to the Earth the distances of those whichhave been thus observed are very much greater than that ofMars , but their minute star-like discs conduce to great accuracyin the measurements made, and the results have agreed verysatisfactorily with those obtained from Mars . Two, namedVictoria and Sappho , will approach sufficiently near to theEarth to be useful in this way during the summer of 1882.It seems likely that the repetition of such observations uponall suitable occasions may in time lead to a very accurateresult.

Upon the whole, it appears that the most probable conclusionto which all our investigations at present tend, is, that the Sun ’sdistance, from the Earth is not far from 93,000,000 miles.This is the value which we shall adopt throughout theselectures. But we cannot, at present, feel any certainty of itsexactness within a T ^th part of the whole value. Nor canwe ever hope to be able to determine so large a measure withabsolute accuracy. The problem, as we have previously stated,is not only a very fascinating one, but is also very difficult.

If by repeated observations of transits of Venus , and by thecomparison of various other methods, we may be able, at somefuture time, to obtain a value true to within a i^^th part, weshall be well content, although this will still leave an un-certainty amounting to nearly 100,000 miles.

It is to be regretted that the nearest distance of the planet Mercury from the Earth is so much greater than that of Venus ,that its transits are of very little use for the purpose in ques-tion. On the other hand, those of Venus occur much less oftenthan we could wish. There will not be another, in successionto that of December 6th, 1882, until the pair which will takeplace in June 2004 and June 2012.

When the vast importance of the Sun ’s distance as the greatunit of astronomical measurement is considered; when weremember that its value is involved in almost every calculationconnected with the solar system, and that it is in terms of itthat we measure our distances from the fixed stars, and the