“For night work I have a diagram to facilitate working the sights of six stars, each of which, in combination with the Pole Star, or each with the other, in certain conditions, will give me a good position. The chief difficulty in getting astronomical positions will be to see the necessary horizon. Should it be visible it will be necessary to know the dip of it, which is approximately the square root of the height of the machine obtained by the altimeter, an instrument in the cockpit indicating the height in feet above the sea-level.
“If I am above the clouds I must judge the height above them and use them for my horizon, which will give useful, if only approximate, results. As a matter of fact, the whole navigation must be considered as an approximation, but as Ireland is large and there are no dangers in the air to keep clear of, I do not anticipate any serious difficulty in making a landfall, given good conditions.”
As regards the weather during the flight, it was not at all as they expected. They anticipated a north-easterly wind for a short way out, backing to the north-west, with a small depression, on the south side of which they expected to pass and thereby get into favourable winds, first westerly and then south-westerly, as they approached Ireland. In actual fact they encountered northerly winds.
At about 7 o’clock Greenwich time, about an hour after the start, the sea was visible through a hole in the fog for just a few seconds. They were then at 4,000 feet and climbing. Grieve, by observing the breaking waves through the drift indicator, was able to calculate the drift of the machine as 10 degrees to the right of their course, precisely the same as when he made his previous calculations just before they passed above the fog.
Until 10.15 p.m. Greenwich time they steered a true east course, not magnetic east. Meanwhile Grieve took sights every half hour, and at 10.15 he estimated that they were 400 miles from St. Johns and had maintained an average speed of 91 miles per hour. They reckoned to be then in the track of the steamships, to keep to which the course was altered to North 73 East true.
The visibility became very bad. In front and to the right and left, above and below, were heavy cloud-banks which formed dark, ominous gorges, or chasms, through which they flew, feeling very, very small and insignificant in comparison with such giants of Nature. That the prospects were not bright was soon proved when they drove into a heavy storm with rainsqualls. A strong northerly gale drove them steadily out of their course and the dense masses of cloud impeded accurate navigation.
It was a lucky stroke of fortune that the engine and all other vital components of the machine survived this bad weather during this early stage as they advanced into night skies.
After flying for five and a half hours, Harry noticed that the temperature of the cooling water in the radiator began to rise. The effect of this, while not appreciable at the moment, was likely to be complex unless the cause, some defect in the circulation, could be remedied. It was, of course, impossible for either Harry or Grieve actually to inspect the likely source of the trouble, and any effort to eliminate it had to be made, if at all possible, by manœuvring the machine.
It was about 11 p.m. Greenwich time (i.e., midnight, summer time) when the defect became apparent. Grieve was busy taking sights while Harry was piloting and watching. The clouds were now exceptionally thick, and Harry recalled that he had only once seen the sea since he was ten minutes’ distant from St. Johns. And he had now been flying for just on six hours.