THE SUN’S DISTANCE.

New Zealand Times, Volume XXXIII, Issue 5374, 18 June 1878, Page 3

THE SUN’S DISTANCE.

To the Editor of The Times, London. Sir, —A few months ago I said that the determination of the sun’s distance, then recently communicated to Parliament namely, 93.375.000 miles—was probably some 800,000 miles too great ; and I spoke of the method on which the determination was based as to some degree discredited by the wide range of difference both between that result and the mean of the best former measurements, and between the several results of which that one was itself the mean. Captain Tupman, as straightforward as he is skilful and zealous, announces as the result of a re-examination of the British observations a distance of about 600,000 miles less than the above, or, more exactly, about 92.790.000 miles, as the sun’s mean distance. But, while he obtains from the ingress observations a mean distance of only 92,300,000 miles, he obtains from the egress observations a mean distance of about 93,040,000 miles ; and the value, 92,700,000 miles, is only obtained as the mean of these two values duly weighted, the egress observations. being more satisfactory than the ingress, observations. I formerly expressed my doubts whether Mr. Stone, Astronomer Koyal at the Cape (to whom the Astronomical Society in 1865 awarded its gold medal for researches resulting in an estimate of about 91,500,000 miles for the sun’s mean distance), would accept the results published by his former chief, the Astronomer Iloyal for England. Strangely enough, the same publication which announces the corrected Greenwich estimate above stated contains a paper by Mr. Stone, in which he deduces from the same British observations during the transit of 1874 a solar distance of nearly ninety-two million miles. Captain Tapman points out that Mr. Stone has not yet seen all the British observations, still this value, deduced from the best of them by a skilful mathematician, well informed as to the sources of probable error, is very significant. He considers that the observations show the distance to lie between 91,400,000 and 92.500.000 miles; whereas at Greenwich no distance much smaller than 92,790,000 miles is regarded as admissible. It seems to mo that the doubts which I formerly expressed as to the trustworthiness of the method employed are to some degree justified. To the general public it will be more interesting to inquire what probably is the true mean distance of the sun. To this it may be replied that in all probability the sun’s distance does not lie so much as 200,000 miles on either side of the value, 92,300,000 miles. Biohakd A, Pkoctoe.