[4] Reproduced, by permission, from Cassell’s ‘New Popular Educator.’
[5] Such objects show considerable glare in a very large instrument. The advent of Jupiter into the field of the 6-foot has been compared to the brightness of a coach-lamp. The outer satellite of Mars was seen twice with this instrument in 1877, “but the glare of the planet was found too strong to allow of good measures being taken.”
[6] My 10-inch reflector by With-Browning was persistently used for four years without being resilvered or once getting out of adjustment.
[7] In this and future references to reflectors the Newtonian form is alluded to. The direct-vision reflectors of Gregory and Cassegrain have gone out of use, and the present popularity of Newtonians may be regarded as a case of the “survival of the fittest.”
[8] Chambers’s ‘Descriptive Astronomy,’ 4th ed. vol. ii., also contains some useful references and diagrams.
[9] The Rev. F. Howlett measured this spot on the following day, June 20, and found it 63″ in its largest diameter. He used a small refractor, and projected the Sun’s image on to a screen sufficiently distant for it to have a diameter of 3 feet.
[10] On May 13, 1890, at 3h, I tested the three methods alluded to on a scattered train of small spots, and derived the following measurements of length:—
By glass micrometer 76,570 miles.
“ cross wires 76,610 ”
“ cardboard disk 75,770 “
In this comparison I used an excellent 4-inch Cooke refractor, belonging to a friend.
[11] The maximum duration of totality, under every favouring circumstance, appears to be about 8 minutes. The great eclipse which occurred on August 18, 1868, maintained the total phase for nearly 6 minutes 50 seconds in the Gulf of Siam. In reference to this eclipse, Dr. Weiss says:—“In the records of ancient eclipses there are to be found only two which may be compared in size with that of August 18, 1868, but none in which the totality lasted so long. The first of these is the eclipse of Thales (28 May, 585 B.C.), which is said to have been the first predicted, and to have terminated a bloody war between the Lydians and the Medes. The second was visible on June 17, 1433, in Scotland, and the time of its occurrence was long remembered by the people of that country as ‘the black hour.’”