* Illustration: Don Clark * We started asking around, and everyone gave us the same answer: "I don't have any data for that," said Amanda Sabia, principal analyst for Internet demand at Gartner Group. "Good question," said Comcast's Mary Nell Westbrook. "We're giving it a look." She got back to us the next day: "We just don't have anything." Apparently it's not something companies study.

Some engineers at Cisco surmised that temperature would affect the conductivity of the copper—and thus the average download velocity of a YouTube video. After all, the Wiedemann-Franz law states that the electrical conductivity of a metal falls as the temperature rises. Since the vast majority of the world's cable is in the northern hemisphere, the warm summertime months above the equator should see a drop in Internet speeds.

"No way," said Doug Webster, a senior director at Cisco. "The infrastructure is engineered to counter those effects." Oh, snap.

Fortunately, his company had the data to end this feud. The networking juggernaut regularly surveys 15 to 20 of the world's largest ISPs. And though Cisco had never crunched the numbers to account for seasonal variation until we asked, its data shows that the bits move most swiftly in June, July, and August.

How could the Internet thumb its binary nose at the laws of physics? Webster has a theory: The Internet runs faster in the summer because people are outside enjoying the nice weather. It turns out that he's right. Traffic has a far greater effect on speed than the weather does. Download- friendly July has the least Web traffic. In 2008, 56 percent fewer bits moved through the Intertubes in July than in September.

Using Webster's logic, you'd think that January and February—when everyone's inside ducking the cold—would have the slowest data-transfer rates. But again, the numbers beg to differ. The Net is most sluggish in September.

Webster didn't have an explanation for this. Sure, schools are in session, but the same goes for February. So we called Harvard economist Jeffrey Miron, who pointed out that this spike corresponds with a well-known phenomenon: "Economic productivity is highest in the autumn."

It makes sense, according to Joe Robinson, who coaches massive corporations like IBM on work-life balance. "I can cite eight studies indicating that performance and productivity go up after vacation," he said. When you return from a long stint at the beach, you're not just recharged, you're more efficient. Even reaction times go up by 30 to 40 percent. It's not surprising then that Internet speeds lag when we're all back from vacay, hustling online, grabbing at that brass ring.

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