That the county commissioners of the respective counties of this state, be, and they are hereby authorized, if in the opinion of the commissioners they shall deem it necessary, to cause the registers of their respective counties, to prepare a general index to all books in their offices, used for the purpose of recording deeds, mortgages and other instruments, in order that the records containing the title of lands, may the more easily be preserved, and a search of said records, to ascertain such title, facilitated; and the said registers shall receive for their compensation such sum as the county commissioners may deem just and right.