Sentence:  Penn was without doubt a man of eminent virtues. He had a strong sense of religious duty and a fervent desire to promote the happiness of mankind. On one or two points of high importance, he had notions more correct than were, in his day, common even among men of enlarged minds: and as the proprietor and legislator of a province which, being almost uninhabited when it came into his possession, afforded a clear <WSD>field</WSD> for moral experiments, he had the rare good fortune of being able to carry his theories into practice without any compromise, and yet without any shock to existing institutions. 
Meaning of the word marked with <WSD> tags:  An unrestricted or favourable opportunity for action, operation, or achievement.