This feeling of discontent with life, or general world-weariness, reached a climax in the concluding years of this period; and its existence in the mind of a small band of practical engineers was certainly the main cause which led to the terrible discovery that placed an indelible line of distinction between the ancient and modern Hesperian histories. Although the northern hemisphere only was accessible for exploration, it was by this time perfectly well known that the planet is a sphere. Hence they considered it not at all improbable that, to the calms of the north, a similar condition in the south might correspond; and that the chronic hurricane which had hitherto barred the passage to the southern ocean might prove to be confined to a zone not exceeding a few hundred miles in width. Should this be the case, it might perhaps be passed, and a southern continent discovered. This would greatly develop astronomical science; nothing less than a hemisphere of unseen stars might be brought into vision. Moreover, a transit of Mercury across the face of the sun would take place in a few years; and, in order to utilise this, a place of observation in the southern hemisphere was essential. It occurred to one of these engineers that, though no ship floating on the surface of the ocean could possibly live in the equatorial tornado, it might be practicable to devise a submarine vessel which, by sinking to a very great depth below the surface, could traverse the four or five hundred miles of raging cataracts, and then, emerging from the depths, might find a smoother sea. It was plain, however, that whoever ventured on such service must be content to incur imminent risk of utter destruction. No one could venture to guess how far downwards the seemingly preternatural disturbance might reach; or what horrors fatal to every form of life might be met in those frightful abysses. So, except for that feeling of weariness of life which was fast growing through the world, it is not at all likely that a body of volunteers, sufficiently numerous, could have been found for a service of such exceeding peril. In one respect, indeed, but only in one, this new enterprise had not as terrible an aspect as that which had been undertaken by the earlier and unsuccessful voyagers to the south. These earlier voyagers had actually ventured on the Infinite, for they had no clue to the shape or extent of their world; but, thanks to the astronomers, it was now well known that the planet is, at all events, bounded in every direction.