WASHINGTON  According to the Congressional Research Service, there are only about 30 scientists among the 535 senators and representatives in the 110th Congress, and that is counting the psychologist, the psychiatrist, a dozen other M.D.’s, three nurses, an engineer, two veterinarians, a pharmacist and an optometrist.

But physics is on a roll.

“Go back 15 years, and there weren’t any physicists,” said Vernon J. Ehlers, a Republican who taught the subject at Calvin College in Grand Rapids, Mich., until he was elected to Congress in 1993.

His was a lone voice until 1998, when Rush Holt, assistant director of the Princeton Plasma Physics laboratory, won election from New Jersey as a Democrat. And today there are three, adding Bill Foster, a physicist at Fermilab and another Democrat, who won a special election in March in Illinois.

“If we continue to reproduce in this manner,” Mr. Foster began, and Mr. Ehlers finished the thought, “the entire Congress would consist of physicists!”