As temperatures in Boston flirted with the century mark yesterday, much of Cambridge and Harvard lost power early yesterday afternoon for a little over an hour and a half because of a malfunction in two electricity transformers.

According to NSTAR, Cambridge’s power distributor, the outage affected 20,000 customers mostly in the M.I.T., Central Square, and Harvard Square areas.

The outage forced many Cambridge businesses to close and forced dozens of Cambridge police officers to direct traffic at the city’s major intersections where traffic lights no longer operated.

On Harvard’s campus, power was lost to most buildings south of the Science Center, including the Allston campus. The outage left virtually all summer school dorm rooms without power and forced the closing of Widener and Pusey libraries.

“Of all the days to have your fan not working, today’s the worst,” said Allison C. Smith, a student in Harvard Summer School’s Secondary School Program.

However, according to Thomas E. Vautin, Harvard’s vice president for facilities and environment services, the loss of power mainly just caused a nuisance for the University—primarily setting off a number of fire alarms.

Another nuisance from the power outage was a flood of old e-mail sent out to undergraduates by the Undergraduate Council’s automated voting system. The UC Vote computer server sent out thousands of messages confirming votes that students had cast in last-year’s council elections.

Council webmaster Jared S. Morgenstern ’03 wrote in an e-mail that when the UC Vote computer rebooted after the outage it caused the delivery of thousands of e-mails which it had previously been unable to send due to a lack of memory.