Section 4. And be it further enacted by the authority aforesaid, That all the provisions of this act, and the act to which this is a supplement, passed the thirteenth April, one thousand eight hundred and seven, be, and the same are hereby extended to the counties of Allegheny, Butler, Mercer, Venango, Warren, Crawford and Erie: Provided however, That said clerk shall not be compelled to serve more than one year in seven.