Hi Vermont,
1. What does 'in the dark of the moon' mean? (--he sould figure up exactly what effect next year's Canada wheat crop woul have on potatoes planted in the dark of the moon.)I'd say it means 'at night'. The usual expression is 'in the dark'. More poetically, you might say 'by the light of the moon'.
2. What does 'straw sailor' mean? (--and she had left the chaplet there, and walked back to the house swinging her straw sailor in her hands.) 'A sailor hat' is a hat similar to that worn by a sailor. Made from straw, in this case.
3. What does 'skies drifting' mean? (In them there were no considerations of Mediterranen cruises, of soporofic Southern skies drifting in the Vesuvian Bay.) 'To drift' means to move slowly, in a current. Clouds drift in the sky. However, because 'cruises' refers to ships, I'd say the reference here is to the idea of a ship drifting along in the Vesuvian Bay.
4. What does 'loafed along' mean? (Sopay, with disgust in his heart, loafed along, twice unsuccessful.) 'To loaf' means 'to be lazy'. 'To loaf along' is to move lazily along.
5. What does 'rule opens' mean? (He arouse, joint by joint, as a carpenter's rule opens, and beat the dust from his clothes.) A carpenter's rule is a long ruler that folds several times so that it will fit in the carpenter's pocket.
Best wishes, Clive