Dear Dr. Boli: Why are vacuum cleaners so loud? —Sincerely, Fido, a Frightened Dog.

Dear Sir: Vacuum cleaners do not naturally make noise. It is a principle well known even to children in grammar school that sound cannot travel in a vacuum; therefore, by a trifling and obvious logical deduction, the mechanism of your vacuum cleaner must be completely silent.

The first marketers of vacuums, however, found that this silence made it almost impossible to sell the things. You may imagine the scene for yourself: the salesman, having cornered his prey at last, prepares to demonstrate the marvelous new invention that will relegate housekeeping drudgery to the history books; with a dramatic flourish he flips the switch, and—as far as the customer can tell—absolutely nothing happens.

It was apparent that, in defiance of all physical laws, the machine must make noise, or it would never be sold; and thus the manufacturers were forced to introduce an artificial noise, which in the earliest models was produced by the inventors themselves screaming into the recording apparatus at the tops of their lungs.

In those early vacuums, the sound was stored on a phonograph record; and before the advent of the electrical process of sound recording, vacuum cleaners had to be quite large, in order to make room for the acoustical reproducing horn. Beginning in the 1950s, the sound was stored on a continuous loop of magnetic tape, which for the first time allowed the housekeeper to vacuum indefinitely without interruption. In modern appliances, the sound is recorded and stored digitally, which makes the manufacture of smaller hand-held vacuum cleaners practical for the first time.

You might suppose that the continuous improvement in the scientific education of ordinary people would render the noise of the vacuum unnecessary, but such appears not to be the case. In spite of our vaunted scientific knowledge, it seems that most of us believe that a machine is more powerful if it makes more noise. The ignorant prejudice of the masses, Dr. Boli regrets to say, is the sole reason why you, and so many of your canine race, must hide under the sofa whenever housekeeping is in progress.