1853.] OF THE ROYAL INSTITUTION. 245 
ranked among the most valuable that has been directed to that subject. 
The historical account of the eclipse is, that the Medes attacked 
the Lydians, and that a war continued several years, until at length, 
when the two armies were preparing for battle, the day suddenly 
became night (an event which Thales is said to have predicted), and 
both parties were so much alarmed that they made peace at once. 
Mr. Baily in the first place pointed out, from a collation of the 
best accounts of total and annular and other partial eclipses, that 
nothing but a total eclipse could produce such a striking effect 
and that a total eclipse could do it. Mr. Baily afterwards saw 
the total eclipse of 1842, but he saw it from the window of a 
house: the Lecturer, who had seen the total eclipses of 1842 and 
1851, in each case from the top of a hill and in command of the 
open country, wished much that Mr. Baily could so have seen it, 
when he could not have failed to be reminded of his former asser- 
tions with regard to the eclipse of Thales: the phenomenon in fact 
is one of the most terrible that man can witness, and no degree of 
partial eclipses gives any idea of its horror. Mr. Baily then, using 
Biirg’s tables, computed all the eclipses which could by possibility be 
visible in Asia Minor through a period of time exceeding that to 
which the eclipse of Thales is limited by chronological considerations, 
and found that only the eclipse of B.C. 610, September 30, could 
be total; and that the track of its shadow would pass across the 
mouth of the river Halys. He accordingly fixed upon that as the 
true date. But he then made a calculation which threw great doubt 
upon the result. Upon using the same tables to compute the eclipse 
of Agathocles (to be described shortly) he found that the track of 
the shadow would be nearly 200 miles in error; and, witha degree 
of good faith which was characteristic of him, he at once avowed 
his belief that if the elements of the tables were so altered as to make 
the eclipse of Agathocles possible, the eclipse of B.C. 610 could no 
longer be shewn to be total in or near Asia Minor. He expressed his 
confidence however that no other eclipse could, under any possible 
change of the tables, have been total in Asia Minor. Mr. Baily’s 
conduct in this avowal was favorably contrasted with that of a German 
astronomer, Oltmanns; who, in one paper, using the same tables as 
Baily, fixed upon the same date as Baily for the eclipse of Thales ; 
and in another paper, after alteration of the elements, shewed that 
the eclipse of Agathocles was possible ; but, although he then alluded 
to his own calculations of the eclipse of Thales, had not the courage 
to announce that his former conclusions must now be considered to 
be unfounded. 
The Lecturer then proceeded to explain how it happens that there 
exists such a connexion between two eclipses nearly 300 years apart, 
that the errors of calculation of one can have any influence upon the 
other. He explained that the moon’s orbit is inclined to the sun’s 
apparent orbit round the earth, but not always in the same direction, 
the line of nodes (or the intersection of the planes of the two orbits) 
