1875.] The Late Transit of Venus. 183 
had also failed, seeing that the duration of the transit could 
not now be determined ; but the essential object in Halley’s 
method is to determine the position of the chord of transit, 
and it still remained possible that this end might be secured. 
Fortunately the clouds which had so long concealed the sun 
cleared partly away about one hour after transit began, and, 
though the sun was visible only for a few minutes, photo- 
graphs and measures were obtained. It was not till 8 o’clock 
in the morning that it became fairly fine, and from that time 
the course of observation steadily proceeded until the end of 
the transit. 
Lord Lindsay’s place was in the photographic room. 
**T took,” he says, ‘‘ 271 plates, out of which number per- 
haps 100 will be of value: cloud and the high temperature 
of the camera were much against me, the temperature 
varying from 96° to r0o0°.. With the heliometer Mr. Gill ob- 
tained five complete determinations of greatest and least 
distance of the centres of the sun and Venus, besides nine 
measures of cusps, and two determinations of the diameter 
of Venus near the end of the transit. Dr. Copeland ob- 
tained fifteen measures of least distance of Venus from the 
sun’s limb, and ten measures of cusps. The last internal 
contact was observed successfully, as also the last external 
contact. 
I come next to a point which I would willingly pass over, 
but that the history of the transit would be incomplete 
without some account of it. It had been shown by me, in 
1869, that Cape Town would be an excellent station for ob- 
serving the middle of the transit. A letter published in 
the “ Times,” for February 15th, from Mr. Dunkin, informed 
astronomers that the egress of Venus was satisfactorily 
observed at Cape Town by Mr. Stone, Astronomer Royal at 
the Cape. The satisfactory observation of egress at Cape 
Town unfortunately counts for very little more than—say— 
the satisfactory observation of a sun-spot on the morning of 
the transit. The valuable stations for egress were those al- 
ready considered, where egress was either notably accelerated 
near E or notably retarded near E. Cape Town is remote 
from either region, and observations of egress there had 
scarcely any value whatever. But Cape Town as a southern 
mid-transit station was absolutely better than any station 
occupied either by our own country or by others. Mid- 
transit photographs secured there, especially with all the 
advantages of a well-provided national observatory, would 
have been invaluable: so, also, would have been heliometric 
measures of Venus at the time of mid-transit, and afterwards 
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