PEORIA — Third-quarter earnings for St. Louis-based Ameren Corp. were down slightly from the third quarter in 2012.Ameren announced net income of $305 million ($1.25 per share) compared to $309 million ($1.28 per share) for the same period last year."Cooler-than-normal weather had a negative impact on third-quarter earnings," said Thomas Voss, Ameren's chairman and CEO in a release.For the first nine months of the year, Ameren's net income [...]