No obstacle intercepted their gaze, which swept the horizon in a semi-circle from the cape to Reptile End.

To the south the horizon, lighted by the first rays of the moon, was very clearly defined against the sky.
At this moment the Southern Cross presented itself to the observer in an inverted position, the star Alpha marking its base, which is nearer to the southern pole.
This constellation is not situated as near to the antarctic pole as the Polar Star is to the arctic pole.

The star Alpha is about twenty-seven degrees from it, but Cyrus Harding knew this and made allowance for it in his calculation.

He took care also to observe the moment when it passed the meridian below the pole, which would simplify the operation.
Cyrus Harding pointed one leg of the compasses to the horizon, the other to Alpha, and the space between the two legs gave him the angular distance which separated Alpha from the horizon.

In order to fix the angle obtained, he fastened with thorns the two pieces of wood on a third placed transversely, so that their separation should be properly maintained.
That done, there was only the angle to calculate by bringing back the observation to the level of the sea, taking into consideration the depression of the horizon, which would necessitate measuring the height of the cliff.