Surrender of governmental power

The fixing of rates which may be charged by public service corporations, of the character here involved, is a legislative function of the state, and while the right to make contracts which shall prevent the state during a given period from exercising this important power has been recognized and approved by judicial decisions, it has been uniformly held in this court that the renunciation of a sovereign right of this character must be evidenced by terms so clear and unequivocal as to permit of no doubt as to their proper construction.