Although the youth of the apprentice did not allow him to pretend to any advanced scientific knowledge, he had the proverbial "weather-eye" of the sailor. He was not only very keen in noticing any change in the aspect of the sky, but he had learnt from Captain Hull, who was a clever meteorologist, to draw correct conclusions from the indications of the barometer; the captain, indeed, having taken the trouble to make him learn by heart the general rules which are laid down in Vorepierre's Dictionnaire Illustré.
There are seven of these rules:-
1. If after a long period of fine weather the barometer falls suddenly and continuously, although the mercury may be descending for two or three days before there is an apparent change in the atmosphere, there will ultimately be rain; and the longer has been the time between the first depression and the commencement of the rain, the longer the rain may be expected to last.
2. Vice versâ, if after a long period of wet weather the barometer begins to rise slowly and steadily, fine weather will ensue; and the longer the time between the first rising of the mercury and the commencement of the fine weather, the longer the fine weather may be expected to last.
3. If immediately after the fall or rise of the mercury a change of weather ensues, the change will be of no long continuance.[1]
4. A gradual rise for two or three days during rain forecasts fine weather; but if there be a fall immediately on the arrival of the fine weather, it will not be for long. This rule holds also conversely.
5. In spring and autumn a sudden fall indicates rain; in the summer, if very hot, it foretells a storm. In the winter, after a period of steady frost, a fall prognosticates a change of wind with rain and hail; whilst a rise announces the approach of snow.
6. Rapid oscillations of the mercury either way are not to be interpreted as indicating either wet or dry weather of any duration; continuance of either fair or foul weather is forecast only by a prolonged and steady rise or fall beforehand.
7. At the end of autumn, after a period of wind and rain, a rise may be expected to be followed by north wind and frost.
Not merely had Dick got these rules by rote, but he had tested them by his own observations, and had become singularly trustworthy in his forecasts of the weather. He made a point of consulting the barometer several times every day, and although to all appearances the sky indicated that the fine weather was settled, it did not escape his observation that on the 20th the mercury showed a tendency to fall. Dick knew that rain, if it came, would be accompanied by wind; an opinion in which he was very soon confirmed by the breeze freshening, till the air was displaced at the rate of nearly sixty feet a second, or more