«Cherished thoughts» of D. I. Mendeleev on population

The scientific legacy of the great Russian scientist D. I. Mendeleev in the field of Economics and sociology is concentrated in his last lifetime books - «Cherished Thoughts» and «Towards the Knowledge of Russia». In this article, the author draws readers» attention to Mendeleev's «law» on the age structure of population. Mendeleev formalized the relationship between the age and the number of a given age group of the population. He proved that the forecast values calculated by him are true on the example of the population censuses of Germany and the North American United States of the late 21st century. Mendeleev connects changes in the age structure of population with the value of the maximum age of survival. The author repeats Mendeleev's calculations using modern methods and information technologies and shows both the advantages and disadvantages of these methods. The author conducts a further study of the population distribution by age based on data from the population censuses of modern Russia and the United States. A dramatic change in the demographic situation a hundred years after the research of Mendeleev is illustrated by the author with graphs of the population distribution by age on the example of modern Russia and the United States. At the same time, the author comes to the conclusion that it is impossible to use Mendeleev's idea of a «sliding parabola» to build demographic forecasts for countries with a modern type of population reproduction. The reason for this is the demographic transition from a progressive to a regressive population structure. According to the author, the second inflection point on the» Mendeleev parabola», which is observed for developed countries, arose not so much due to a decrease in the birth rate, but due to government support measures. Nevertheless, Mendeleev's parabola can be used as a tool for demographic forecasts for countries and separate regions with a progressive population structure.