Thermo Instrument Systems Inc. has commenced, through...

Thermo Instrument Systems Inc. has commenced, through a wholly owned subsidiary, a cash tender offer for all outstanding shares of common stock of San Jose-based Finnigan Corp. at $20 per share . . . The Federal Reserve said the average yield for one-year T-bills, the most popular index for making changes in adjustable-rate mortgages, rose to 8.57% last week, up from 8.41% the week before . . . The number of working U.S. oil and natural gas rigs is down for the fourth straight week, slipping by five in this week’s tally to total 927, Baker Hughes reported. There were 761 rigs counted at this time a year ago.