The Reserve Primary Fund, the giant money market fund whose customers have been waiting more than six weeks for their cash, announced late Thursday night that it would begin mailing checks to shareholders on Friday — for half their original investment.

The announcement was the first indication of the losses the fund sustained when a wave of redemptions on Sept. 15 forced it to freeze withdrawals and liquidate its assets. The next day, the fund said it had "broken the buck," reporting a per-share value of less than a dollar.