He then commenced the study of law under David Kinney, Esquire, at New Castle, Delaware. He explored the vast field of this science with astonishing and unusual success, and was admitted to the bar under the most favourable auspices. He commenced practice at the same place, and soon acquired a lucrative business and a proud reputation. He extended his operations into the province of his nativity, and was admitted in the Supreme Court of Pennsylvania, in 1757. His strict attention to business and his superior legal acquirements, obtained for him an extensive and just celebrity. Although he had become the eloquent advocate and able lawyer, he was still a close and industrious student. He continued to add to his large stock of knowledge, with the same avidity and to greater advantage, than when he commenced his scientific career. He did not fall into the error that has prevented some lawyers of strong native talent from rising above mediocrity: _that when their practice begins their studies end_. This is a rock on which many have been shipwrecked in all the learned professions. The laws of nature demand a constant supply of food in the intellectual as well as in the physical world. The corroding rust of forgetfulness will mar the most brilliant acquirements, of literature, unless kept bright by use; and much study is requisite to keep pace with the march of mind and the ever varying changes in the field of science, constantly under the cultivation of the soaring intellect of man. It maybe said, that the grand basis of the law is as unchanging as the rock of adamant. To this I answer: its superstructure is an increasing labyrinth, and, unless the progress of the work is kept constantly in view, those who enter, strangers to its meanderings, will find themselves in a perplexing situation. In 1762, Mr. M’Kean was elected a member of the Delaware assembly from New Castle county, and was continued in that station for eleven successive years, when he removed to the city of Philadelphia. So much attached to him were the people of that county, that they continued to elect him for six succeeding years after his removal, although he necessarily declined the honour of serving. He was claimed by Delaware and Pennsylvania as a favourite son of each, under the old regimen, and did, in fact, serve both after changing his residence, by being elected to the continental congress from the state of Delaware, being then Chief Justice of Pennsylvania, the former state claiming him, probably, because he still retained his mansion, furnished by himself, in New Castle, where his business frequently called him.