TOTAL SOLAE ECLIPSE OE JULY 18, 1860. 
411 
The edge a of the prominence A (the cauliflower or wheatsheaf) is not far from a line 
at right angles to the path of the moon’s centre, and is well situated, therefore, for 
ascertaining whether the change of position-angle accords with the demands of that 
hypothesis which assumes that the luminous prominences belong to the sun. 
Disregarding, for the moment, the errors in the assumed places of the wires, we have 
the following results. 
Position of the prominence A, measured on the edge a : — 
Original negative . 
Albumen positive . 
Difference . . 
Eirst totality-picture. 
Second totality-picture. 
28 10 
o / 
22 15 
27 47-5 
22 37 
- 22-5 
+ 22 
Angular shift. 
O / 
5 55 
5 10-5 
Both these values of the angular shift have to be diminished by 1', in consequence of 
the alteration of the position-wires of the instrument in the interval between the two 
epochs, and they become respectively 5° 54' and 5° 9'-5. 
Considering the difiiculties experienced, from the causes before mentioned, in making 
measurements of position-angle, it is quite justifiable to take the mean of the above 
results ; for, besides the uncertainty in determining the exact boundary of a prominence 
in the photograph, there is superadded, also, the difficulty of placing the photograph, 
quite correctly, in its proper angular position on the measuring-instrument, on account 
of the wires being very faintly imprinted on the western side of the picture in the first, 
and on the eastern side in the second, totality-picture. 
The mean of the two measures gives 5° 32' as the angular shift in the position of 
prominence A. Assuming, in accordance with theory, the motion of the moon’s centre 
to have been 92"'8 during totality, we have 5° 21' as the theoretical change of position- 
angle, which, deducted from the mean 5° 32', gives the difference of 0° 11'. 
On taking an average of the measurements of all the prominences, the difference 
between the measured and the computed angular shift is only half this quantity, as 
will presently be seen. 
Table VII. 
Table VII. contains the results of measurements of positive photographs 9 inches 
in diameter. Columns 4, 5, 6, 7, and 8 relate to No. 1 totality-picture ; and columns 9, 
10, 11, 12, and 13, to No. 2 totality picture. Columns 7 and 12 show, respectively, the 
differences in the determinations of the position-angles of the several prominences in 
No. 1 and No. 2 totality-pictures, on the 9-inch photograph and the original negatives 
and positive-albumen copies by superposition. I give preference to the measures by 
means of the instrument of the original negatives and the direct albumen copies, so far 
as regards the position-angles ; but for measuring the amount of motion of the moon’s 
centre during the totality, I am, for the reason already assigned, dependent on the 
9-inch photographs. The whole difiiculty, with respect to the latter, consisted in 
exactly ascertaining the position of the centre of the moon in the two pictures, and in 
measuring correctly a picture of the sun, enlarged to the same scale, with a divided 
