TOTAL SOLAE ECLIPSE OE JULY 18, 1860. 
415 
In conclusion, the two totality-pictures No. 25 and No. 26, when reduced to a suit- 
able size and placed in the stereoscope. No. 25 on the left, and No. 26 on the right, 
afford a very beautiful view of the phenomena of totality, and one which could not be 
enjoyed by mortal eyes in looking at the real eclipse. Not only does the stereoscope 
render evident the fact of the moon being an object intervening between the observer 
and the sun, but it also shows it as a sphere. The triplication of the prominences 
must be corrected in No. 26 ; but any attempt to complete the lunar disk by painting 
on a positive copy, as a, ( 3 , and y photographs, the originals of Plates X., XI., and Xll., 
is immediately detected, and the corrected lunar disk appears perfectly flat. In placing 
the photographs in the stereoscope, the prominence A must be placed upwards, and at 
right angles to the line joining the centres of the photographs. 
Appendix. 
Having brought to a successful issue the photographic record of a total eclipse, it may 
not be out of place to point out for the guidance of others what steps I would recom- 
mend should hereafter be adopted. 
In the foot-note to p. 334, I have mentioned that with my 13-inch reflector intense 
photographs of the moon were obtained in four seconds, and that, under precisely similar 
atmospheric circumstances, it required three minutes to obtain a feeble impression of the 
moon with the Kew heliograph, which, for the present, is mounted on an outrigger 
attached to the declination axis of my reflector. It will be remembered that for the totality- 
pictures obtained at Rivabellosa, under exceptionally favourable conditions in respect of 
the sun’s altitude and the state of the atmosphere, the sensitive plate was exposed exactly 
one minute, the resulting photograph being remarkably dense, even to a fault. A picture 
of the moon, of greater intensity than the feeble image given by the Kew heliograph, 
could be obtained with my reflector in a second, so that it would produce pictures of 
the prominences in the time required by the heliograph, or in 
of a second. Making suflicient allowance for the difficulties in determining the exact 
ratio of actinic intensity in the foci of the two instruments, and also for a condition of 
the atmosphere less favourable than that under which the ‘Himalaya’ photographers 
worked, it may be safely estimated that, with a 1 3-inch reflector, perfect pictures of the 
prominences could be procured in two seconds. A 13-inch reflector would, however, be 
a cumbrous instrument to transport and erect at a distance from home ; but a 9-inch 
reflector — or its equivalent, a 6-inch refractor, specially corrected for the actinic rays, is 
within the compass of such an expedition. These telescopes might be mounted with 
clockwork drivers on rigid equatorial stands, which must, however, be so designed as 
to admit of an adjustment of the polar axis to suit various latitudes. For each instru- 
ment an observatory should be constructed to take to pieces. Each observatory would 
require not less than four plate-holders, and about six baths to contain nitrate of silver, 
