PAST AND COMING TRANSITS AND ARCTIC EXPLORATION. 273 
one station was specially suited for mid-transit photography — 
Cape Town. Though Natal would have been worth occupying, 
Cape Town was superior to' every other southern station for this 
particular purpose. But somehow the suggestion that photo- 
graphs should be secured there was overlooked, and a new cause 
of regret added to several which will be recognised by those 
who come after us as they scan the history of the late transit. 
But in 1882 this method— the mid-transit photographic 
method — will be the one on which, I venture to predict, chief 
reliance will be placed. Owing to the long duration of that 
transit (exceeding, by two hours, the duration of the recent 
transit), it will be impossible to find any pairs of stations, 
northern and southern, at each of which the whole transit will 
be favourably seen. This will be manifest from figs. 1 and 2, 
showing the face of the earth, turned sunwards, at the begin- 
ning and end of 'the ' transit of 1882. It will be seen that, 
though the dotted stations in the north will be well placed 
throughout the transit, there are no southern stations well 
placed for both the beginning and end. For to be well placed 
they ought to be at once near A of fig. 1, and near D of fig. 2 ; 
and these two points (owing to the long duration of the transit) 
are far apart on the earth’s surface. The points marked 1 and 
2 are those best placed in a geometrical sense ; and these were 
indicated, eleven years ago, by the Astronomer Royal, as points 
one or other of which ought to be occupied by Great Britain in 
1882. But apart altogether from the difficulty of occupying 
these stations on the antarctic continent, they are neither of 
them well suited for observing both the beginning and end of 
transit ; the sun being very low at both stations at the begin- 
ning of transit, and at one of them at the end of transit also. 
So far, then, as the older methods of observing transits are con- 
cerned, the transit of 1882 can only be observed by Delisle’s 
method. But we have seen that contact observations cannot be 
relied upon for improving our knowledge of the sun’s distance. 
And if they could not be relied upon for that purpose now, 
still less can they be relied upon in 1882, before which time 
astronomers will have secured valuable determinations of the 
sun’s distance from observations of the planet Mars, during the 
singularly favourable opposition of 1877.* . 
But mid-transit can be advantageously recorded by photo- 
generosity, consistel in denunciations addressed to me for overlooking the 
point which had appeared to myself and others too obvious for special 
mention. 
* It may well be hoped that stellar photography will be employed to 
obtain records of the position of Mars among the stars on that occasion. This 
method seems to promise better results than any other yet applied, or at 
present available. 
VOL. XIV. NO. LVI. T 
