12

THE SUN.

the observations only determined the probable value to besomewhere between 92,000,000 and 92,700,000 miles.

There is no doubt that the discordances of these results chieflydepend upon the different interpretations that have been givento the actual wording of the reports of the observers. In sayingthis, we do not for a moment wish to disparage the value oftheir work, or of the observation of transits of Venus for thepurpose in question ; but it must be confessed that there is atpresent an amount of uncertainty in the figures obtained,which is disappointing, but which seems likely to continue,unless we can in some way improve our instruments, or themethod of their use.

It must also be a subject of great regret that the numerousphotographs of the transit which were taken by the BritishExpeditions in 1874, have not been found to depict the edgesof the Sun and of the planet with sufficient sharpness to allowof any very accurate calculations being made from them.

It has, however, been recently suggested by Mr. Maunder, ofthe Royal Observatory, Greenwich, that iu the transit of 1882Venus may pass sufficiently near to some clearly defined sun-spot, to allow the measurements of its position in a photographto be made with greater accuracy from the edge of the spot,instead of from the edge of the Sun’s disc.

V e may still obtain some further information from a com-parison of the British results with those of other nations ; ofwhich, as yet, we know comparatively little, but it seems, sofar as transit observations are concerned, that an uncertaintyamounting to at least 500,000 miles will most probably remain.A preliminary discussion of the American photographs by Mr.D. P. Todd, in the Journal of Science, of June 1881, which,owing to the special method by which they were taken, are,we believe, capable of a more precise interpretation than thoseof the British Expeditions, seems to indicate a value of a littleover 92,000,000 miles.*

Upon the whole it is very uoticeable that all these values,deduced from the transit of 1874, are much nearer to the

* It is also gratifying to know that the American photographs of thetransit of Mercury in 1878 have proved very successful.