A century earlier, Henry Cavendish had noted the existence of a residual gas when oxygen and nitrogen are removed from air, but its importance had not been realized.
That's because very large animals have a slow rate of reproduction, so all you have to do is remove a few young females from the herd, and you can, fairly quickly, significantly reduce the population.
Once a generation of young people has obtained a good knowledge of physics, music or English we don't just dust off our hands and go home – we move on to the next.
They looked at death rates by county, having corrected for migration and merged sparsely populated ones so that America's 3, 141 counties became 2, 068 “county units”.
They looked at death rates by county, having corrected for migration and merged sparsely populated ones so that America's 3,141 counties became 2,068 "county units".