A dozen years ago, hot dogs and peanut butter were about the only affordable fare for Bruce Bent and Henry Brown, the inventors of the money-market mutual fund. Their creation, registered in 1971 as the Reserve Fund, offered big yields to small savers for the first time and eventually spawned a $200 billion industry. At the outset, the idea yielded Brown and Bent little besides frustration, but nowadays they are a couple of happy millionaires.
The two men were partners in a financial consulting business in 1969 when they observed that it was possible to get 8% or 9% on short-term investments...