And during the siege there were sixty-five balloon flights carrying two and a half million letters, weighing a grand total of 10,000 kilograms, so roughly about 20,000 pounds.

在巴黎被围期间,共放出了六十五个热气球,带走了多达两百五十万封信,合计重量约有一万公斤,也就是两万磅左右

耶鲁公开课 - 1871年后的法国课程节选