Calculating France's population in 1781–1782 ----------------------------------------------------
In a paper presented to the Académie royale des sciences in 1783 and published in 1786, Laplace states that "it is of interest in every respect to know the population of France, to track its growth, and to determine the law governing how people are distributed across the surface of this great Kingdom". He therefore introduces a method for calculating the population without conducting an exhaustive census of every individual.
Laplace has the birth records for 1781 and 1782. He proposes calculating the ratio of the number of people to the number of births "in a large number of parishes selected from every province of the Kingdom". He then need only multiply the country's total number of births by this ratio.
"The censuses already conducted in France, when compared with the births, give approximately 26 as the ratio of population to births; now, taking the average number of births in 1781 and 1782 gives 973,054½ annual births […]; multiplying this number by 26 therefore gives a population of 25,299,417 for the whole of France."