THE SUN’S DISTANCE.

Globe, Volume IX, Issue 1255, 15 March 1878, Page 3

THE SUN’S DISTANCE.

The following letter from the well-known astronomer, R. A. Proctor, on the results of the British Transit Expeditions, was published in the “ London Times” of December 18th : —“ I have received a. large number of letters respecting the new estimate of the Sun’s distance tieducible from the observations of the British Transit Expeditions. Among these letters is one from the author of a. forthcoming work on astronomy, who wishes to know whether all the dimensions depending on the Sun’s distance ought now to be modified to accord with the new evaluation. It may probably be of use to indicate how the matter at present stands. The value of the Sun’s distance, deduced by Captain Tupman with great skill and after much labour from many sets of observations made with much care and after long practice, may be set at 93,321,000 miles. The sole method employed in obtaining this result has been that called Delisle’s, which, between 1868 and 1874, was the subject of so much controversy in these columns and elsewhere. In fact, the observations employed may be said to belong exclusively to Sir G. Airy’s original scheme. For the Halleyan observations made at southern stations by the British parties will be effective only when combined with those made at northern stations by America, Russia, and Q-ermany. This result, 93,321,000 miles, exceeds by very nearly a million miles Newcomb’s mean value (92,393,000 miles) deduced from observations by six methods. It exceeds by more than a million miles Lcverrier’s estimate from the planetary perturbations. It exceeds still more (by about 1,800,000 miles) the value for deducing which from the transit observations of 1769, Stone (then first assistant at Greenwich) received a few years ago the gold medal of the Astronomical Society. “ The probable error of the new result is set by Captain Tupman at 200,000 miles. It is a rather significant circumstance, however, that of the two sats of observations (ingress and egress) into which the British results can be divided, one gives a distance exceeding by more than a million miles the distance given by the other set. “ It appears to me that the main result'of the observations is the demonstration of what was before a matter of surmise—the untrustworthy nature of Delisle’s method.”