Mass. Gen. Laws ch. 217 § 3B
There shall be an associate justice of the trial court appointed in Hampshire county, hereinbefore known as the special judge of probate and insolvency in the county of Hampshire, who shall be and perform the duties of a full-time circuit justice in said county or such other county as the chief justice may designate, and when so assigned shall receive from the commonwealth the expenses incurred by him. Upon such designation, the registry of the court to which said circuit justice is assigned shall certify upon the records of the court, and to the comptroller, the number of days, the dates upon which, and the occasions for which, the circuit justice performed his duties. Nothing in this section shall be construed to establish a new judicial position nor abolish the tenure of the incumbent special judge of probate and insolvency.
Mass. Gen. Laws ch. 217, § 3B