1868. | Astronomy. 69 
Gulf of Siam, when it reaches on the central line no less than 6’ 50", 
the altitude of the sun being 873°. On its further progress, the 
shadow runs through Borneo, Celebes, the Islands Bouru, Am- 
boyna, Ceram, and the Arrou Archipelago; covers completely the 
southern part of New Guinea, and moves then towards the New 
Hebrides, where the totality begins at sunset. 
What renders this eclipse so important an object of attention 
to astronomers, is the fact that the totality lasts almost as long 
as is possible under any circumstances. For at the commencement 
the Moon will have just passed a perigee of uncommon proximity, 
and she reaches during the eclipse the ascending node of her orbit. 
Thus the eclipsed sun rises nearly to the zenith of those countries 
where the eclipse takes place at noon; and therefore the aug- 
mentation of the moon’s diameter (due to her altitude) is a 
maximum, and the rate at which the shadow sweeps over the 
surface of the earth is a minimum. ‘The result of the coincidence 
of all these favourable circumstances will be an eclipse without rival 
in the records of past eclipses. ‘There are to be found only two 
which may be compared in size with that of August 17, 1868, and 
none in which the totality lasts so long. ‘The first is the eclipse of 
Thales (May 28, 585 3.c.), said to have been the first predicted, 
and to have concluded a fierce engagment between the Medes and 
Lydians. The second was visible on June 17, 1435, in Scotland, 
and the time of its occurrence was long remembered by the people 
of that country as “the black hour.” 
But besides its enormous size, the eclipse deserves special atten- 
tion in another respect. In researches on the nature of the red 
protuberances and other phenomena visible during total solar 
eclipses, it would certainly be of the highest importance to learn 
something about the nature of changes to which these appearances 
may be subject. On a single place upon the shadow’s path, the 
time of visibility is too short to permit of the hope of perceiving 
processes of physical change in these objects; but it is far from 
being improbable that observations, obtained at several places along 
the line of totality, might afford the information we seek on this 
point. In the present instance the shadow touches a series of 
accessible regions, as we haye seen. It is also very probable that 
favourable weather will prevail at the time of observation. 
It would certainly be well that efforts should speedily be made 
to take advantage of so favourable an occasion for extending our 
knowledge of solar physics. Centuries will pass before we have 
such another opportunity. 
Turning to Major Tennant’s remarks on the subject of the 
same eclipse, we find that much has been done in the way of pre- 
paration. The Council of the Astronomical Society has decided that 
there should be provided for photography a silvered-glass reflector, 
