The sea, to one looking across it, would have appeared of a beautiful indigo tint; but if one gazed straight down into the water, it seemed opaque in the purple blackness of its profundity, as if the perpetual night that reigned in the mysterious depths below were sending its shadow upwards to the surface. Yet so perfectly translucent was that ink-like water that any bright object, such as a plate, thrown into it would remain distinctly visible as it slowly descended--yes, even till it was so far down that it seemed no larger than a small coin. The yacht _Petrel_ lay becalmed on the tropical sea. All her canvas had been lowered, and she floated idly, while the fierce, vertical sun was blistering the paint on her sides, and the melting pitch oozed from the seams of her decks. For thirteen days she had been drifting thus on a windless ocean, her crew languid and irritable from the stifling heat, which it is impossible to mitigate on a small craft, waiting for the breeze that never came. For thirteen days of unbearable calm, broken only by occasional brief squalls, accompanied by torrential downpour of rain, and thunder and lightning of appalling grandeur--squalls which raised the flagging hopes of the men for a space, and to which they hastily hoisted their canvas, that they might be carried out of this dismal tract of the ocean; but after they had been driven on their way a mile or two only, the wind would suddenly drop again, the dark clouds would clear away, and the sun would blaze down fiercer than ever out of the implacable sky. The _Petrel_ had reached the region of the equatorial calms, the sultry Doldrums dreaded by the sailor, that broad belt of sluggish sea that divides the tract of the north-east trade wind from that of the south-east. Here the aërial currents neutralise each other and are at rest--a desolate, rainy ocean that lies under an almost stagnant atmosphere of steaming heat, where vessels have lain becalmed for wearisome week after week; even, in many cases, until the supply of fresh water had been exhausted and the men perished of thirst. And yet to the northward and to the southward the fresh trade winds blow perpetually in one direction, across vast stretches of ever-tossing waves. The voyage of the _Petrel_ had been a very prosperous one up to this point. She had met with fair winds for the most part until she reached the limits of the north-east trades, which, blowing right aft, had carried her on her way at the rate of nearly two hundred miles a day. Carew had sighted Madeira and the westernmost islands of the Cape Verde archipelago; but as the yacht was well provided with provisions, he had not called at any port. After having been a little over a month at sea, he had entered the calm region about the equator, and here, as I have said, scarcely any progress was made for a fortnight.