“When stocks are down big, stick with the long-term themes that work,” Jim Cramer told fans of his “Mad Money” TV show Tuesday. Cramer advised investors to stick with long-term themes he has been mentioning like agriculture, oil and gas, infrastructure, minerals and aerospace. Cramer also said investors should buy his new-tech stock names like Eaton (ETN), Parker Hannifin (PH), Emerson (EMR), and First Solar (FSLR). Cramer explained that these new-tech stocks are solving the worlds top 10 problems – energy, food, water, the environment, poverty, fighting terrorism, disease, education, democracy and population. He feels these stocks are exactly where investors should be putting their money when the market sells off. “These are the themes that let you sleep at night without nightmares,” Cramer said.