four o'clock
The Professor concurred in this as the most liable to give them the best results , as they were out for the purpose of making tests of the craft on the open sea . After sailing for an hour along the coast to the south , the shore line turned to a southwesterly direction , and the mountain range was now clearly perceptible , extending southwest , and along which it appeared that the coast followed . The wind changed and came from the mountains , and made progress slow . There was also a decided change in the temperature , and by four o'clock it was impossible to follow the coast except by constant tacking . The boat was turned to the north , and with the strong wind , which had now perceptibly increased , began to make good time . As evening approached , the wind increased , until it blew with considerable violence , every minute being more boisterous , and the Professor suggested that the jib be taken down , which was done ; but the increasing gale , and the terrible strain on the mast and sail , made the boys look inquiringly at the Professor , for a word of warning . He sat there grimly during the raging storm , and with the halliards gradually let down the mainsail when the tempest had reached such a point that it appeared to sweep everything from the boat .