Commentary The yield curve measures the difference between short-term borrowings, or “short” money, and “long” money, borrowed on longer terms. The Fed typically affects interest rates by setting the overnight borrowing rate for member banks. Open Market Operations, its second principal means of moving rates,  affects cash in the economy by selling Treasurys to pull money out of the economy and thus raise interest rates.  To lower rates, the Fed buys Treasurys to add money to the economy.  Finally, the Fed can raise or lower member banks’ reserve ratio, the amount of money a bank must keep on deposit at the Federal Reserve to affect the money supply. But all those Federal Reserve measures typically affect just shorter-term rates; longer-term rates tend to be more market dependent. And there’s the rub. In a healthy economy, long money comes with a higher interest rate than short money because the lender’s money …