a
plate of tourmaline. This plate of tourmaline can be turned round by the
observer. In one position it hardly interferes with the polarised light
at all, while in the position at right angles thereto it cuts off nearly
the whole of it. By simply adjusting the position of the tourmaline, the
observer has it in his power to render the image of any brightness that
may be convenient, and thus the observations of the sun can be conducted
with the appropriate degree of illumination.

But such appliances seemed on this occasion to be a mere mockery. The
tourmaline was all ready, but up to one o'clock not a trace of the sun
could be seen. Shortly after one o'clock, however, we noticed that the
day was getting lighter; and, on looking to the north, whence the wind
and the snow were coming, we saw, to our inexpressible delight, that the
clouds were clearing. At length, the sky towards the south began to
improve, and at last, as the critical moment approached, we could detect
the spot where the sun was becoming visible. But the predicted moment
arrived and passed, and still the sun had not broken through the clouds,
though every moment the certainty that it would do so became more
apparent. The external contact was therefore missed. We tried to console
ourselves by the reflection that this was not, after all, a very
important phase, and hoped that the internal contact would be more
successful.

At length the struggling beams pierced the obstruction, and I saw the
round, sharp disc of the sun in the finder, and eagerly glanced at the
point on which attention was concentrated. Some minutes had now elapsed
since the predicted moment of first contact, and, to my delight, I saw
the small notch in the margin of the sun showing that the transit had
commenced, and that the planet was then one-third on the sun. But the
critical moment had not yet arrived. By the expression "first internal
contact" we are to understand the moment when the planet has completely
entered _on_ the sun. This first contact was timed to occur twenty-one
minutes later than the external contact already referred to. But the
clouds again disappointed our hope of seeing the internal contact. While
steadily looking at the exquisitely beautiful sight of the gradual
advance of the planet, I became aware that there were other objects
besides Venus between me and the sun. They were the snowflakes, which
again began to fall rapidly. I must admit the phenomenon was singula