The Faculty of Arts and Sciences (FAS) will continue to grow, and appointments in science and engineering will fuel the bulk of that growth over the next few years, outgoing Dean of the Faculty Jeremy R. Knowles wrote in a letter to professors yesterday.

Knowles, a chemist and an interim dean three months away from stepping down from the post, identified a dearth of scientists and poor student-faculty ratios as problems that should inform the future expansion of FAS. As new, high-cost science buildings go up in the North Yard, the stage seems to be set for an influx of scientists and engineers into the Faculty—nearly two years after former FAS dean William C. Kirby unexpectedly slowed Faculty growth.

In his letter, Knowles did not say specifically how many professors should be added in the coming year, and a spokesman said Knowles was unavailable for comment yesterday afternoon. But his letter emphasized faculty hiring that he said will keep FAS “of the first rank” in cutting-edge fields such as genomics and nanotechnology.

“Looking ahead, a larger Harvard science faculty must comprise a richer mixture of large and small science, of theoretical and experimental research, and of individual research groups and collaborative, boundary-crossing activity,” Knowles wrote.

The dean said scientists also had to be hired with an eye to improving how their disciplines are taught to undergraduates, concentrators and non-concentrators alike. “We must bring more of our non-science students to a more confident engagement with science,” he wrote.

Underscoring the need for continued expansion, Knowles presented a bar graph showing last year’s ratio of 14.6 students per “ladder” faculty—tenured and tenure-track professors—as compared to 9.9 students at Yale (in 2004-2005) and 10.7 students at Princeton. Stanford and UC Berkeley, on the other hand, were shown to compare unfavorably with Harvard’s ratio.

The number of faculty members with ladder positions has grown from 615 to 723 over the last decade—a larger increase than the last four decades combined, according to Knowles’s letter.

New hires in the social sciences and arts and humanities accounted for most of that growth, Knowles said, and FAS now lags behind Yale, Princeton, and Stanford in the proportion of faculty in the natural sciences.

A number of professors, scientists and non-scientists alike, said yesterday they hadn’t yet read Knowles’s letter. But one who had, former Germanic Department Chair Judith L. Ryan, said she was surprised to learn that humanities departments at Harvard had been growing.

Ryan, the Weary professor of German and comparative literature, said that she still had the impression that humanities departments at Harvard were smaller than their counterparts at peer institutions, and, as a result, professors’ time was stretched thin.

“I wish that I could be cloned three times,” Ryan said. “I wish there were three of me.”

At FAS this year, social sciences and humanities professors total 460, while professors in the physical sciences, life sciences, and the School of Engineering and Applied Sciences number 263.

Knowles stressed that as FAS grows, the distribution of professors across the disciplines should be motivated not by the need for teachers alone, but also “to achieve a deeper range of scholarly excellence.”

“Even if (let us say) there was hardly any student interest in physics or philosophy, it would be quite improper not to have the best Physics or Philosophy departments that we could build,” Knowles wrote.

As he put it, “We are a Faculty, not a factory.”

—Staff writer Carolyn F. Gaebler can be reached at cgaebler@fas.harvard.edu.