As the horizon is often obscured by clouds or mist, making impossible the measurement of its angle with the heavenly bodies, I had a special type of spirit level, on which the horizon was replaced by a bubble. This, of course, was less reliable than a true horizon since the bubble was affected by variations of speed; but it was at least a safeguard. Taking into account the general obscurity of the atmosphere during most of the flight, it was fortunate that I took such a precaution, for I seldom caught sight of a clearly defined horizon. I could legitimately congratulate myself on having collected as many early observations as possible while the conditions were good; for soon we ran into an immense bank of fog, which shut off completely the surface of the ocean. The blue of the sea merged into a hazy purple, and then into the dullest kind of gray. The cloud screen above us, also, grew much thicker, and there were no more gaps in it. The occasional sun-glints on wing-tips and struts no longer appeared. Thus I could obtain neither observations on the sun, nor calculations of drift from the seas. Assuming that my first observations were satisfactory, I therefore carried on by "dead reckoning," and hoped for the best. From time to time I varied the course slightly, so as to allow for the different variations of the compass. Meantime, while we flew through the wide layer of air sandwiched between fog and cloud, I began to jot down remarks for the log of the journey. At 5:20 I noted that we were at fifteen hundred feet and still climbing slowly, while the haze was becoming ever thicker and heavier. I leaned towards the wireless transmitter, and began to send a message; but the small propeller on it snapped, and broke away from the generator. Careful examination, both at the time and after we landed, showed no defect; and I am still unable to account for the fracture. Although I was too occupied with calculations to pay much attention to moods or passing thoughts, I remember feeling that this cutting off of all means of communication with the life below and behind us gave a certain sense of finality to the adventure. We continued eastward, with the rhythmic drone of the motors unnoted in supreme concentration on the tense hours that were to come. CHAPTER IV EVENING For a time Alcock and I attempted short conversations through the telephone. Its earpieces were under our fur caps, and round our necks were sensitive receivers for transmitting the throat vibrations that accompany speech. At about six o'clock Alcock discarded his earpieces because they were too painful; and for the rest of the flight we communicated in gestures and by scribbled notes.