184 The Late Transit of Venus. (April, 
until the end of the transit. It appears only too certain, 
from the absence of all mention of any such work in Mr. 
Dunkin’s letter, that absolutely no provision whatever had 
been made for these most important purposes.* If the 
opportunity of utilising the Cape Town Observatory for 
mid-transit observations had simply been overlooked, little 
need have been said. That would have been no novelty, un- 
fortunately. But special attention had been directed to the 
value of the station. In reply to a letter by Admiral Sir H. 
Cooper Key, inquiring whether Sir G. Airy had made arrange- 
ments for photographing mid-transit, the answer came that 
the method had been amply provided for; yet at the very 
best station for the purpose no provision had been made, though 
the station was exceptionally suitable, because of the Govern- 
ment Observatory there and the presence of skilled astrono- 
mers. This would have been unfortunate as a mere case of 
negligence, but in its real aspect the matter is much more 
serious. It will not readily be forgotten. 
In summing up the results of Halleyan and mid-transit 
operations, we must distinguish between contact observa- 
tions, photographic results, and heliometric measurements. 
We must also draw a distinction between the various modes 
of photographing the transit employed at different stations. 
It seems probable that in future transits less reliance will 
be placed on contact observations than on photographic 
work. It is true that the results obtained during the recent 
transit show that the phenomenon of the ‘‘ black drop,” 
which in 1761 and 1769 occasioned so much trouble, depends 
on instrumental imperfections and atmospheric disturbances,T 
and can be practically eliminated by employing good tele- 
scopes and choosing stations where the sun will not be too 
low at the time of either internal contact. Nevertheless, a 
‘personal equation”? comes in, depending on the fact that 
the eye itself is part of the optical arrangement for observing 
* It is impossible not to connec this with what happened in the case of the 
important total solar eclipse of April, 1874, when totality lasted more than 
four minutes. On that occasion, though the track of total shadow passed 
close by our Cape Colony, Mr. Stone received no assistance whatever towards 
the proper observation of the eclipse. He had not even an equatorial tele- 
scope; but was obliged to observe with an altazimuth telescope ‘‘ borrowed 
from Mr. H. Solomon,” to which Mr. Stone attached a spectroscope with 
‘* wrappers of wash-leather,”’ for want of more suitable appliances. 
+ Mr. Stone’s ideas on this subje@t, on which so much stress was laid in 
1868, have been entirely overthrown by the recent transit observations. Of all 
whose results have reached us, Mr. Stone himself was the only observer of skill 
who, with a good telescope, saw any approach to the “ black drop ” required by 
his theory. Certainly he saw and pictured what accorded most perfectly with 
his own ideas; but that only shows how likely preconceived opinions are to 
make the observer fancy he sees what he thinks he ought to see. 
