The Evolution of Welfare Economics

Edgeworth defines exact utilitarianism to entail the greatest quantity of happiness of sentients, exclusive of number and distribution — an end to which number and distribution are but means.
Utility, as Professor Jevons says, has two dimensions, intensity and time. The unit in each dimension is the just perceivable increment. The implied equation to each other of each minimum sensibile is a first principle, incapable of proof.
Mathematical Psychics (1881) p.7
Problem.—To find $(\alpha)$ the distribution of means and $(\beta)$ of labor, the $(\gamma)$ quality and $(\delta)$ number of population, so that there may be the greatest possible happiness. … Greatest possible happiness is the greatest possible integral of the differential 'Number of enjoyers${}\times{}$duration of enjoyment${}\times{}$degree thereof '….${}^2$
${}^2$ The greatest possible value of $\int\int\int dp\,dn\,dt$ (where $dp$ corresponds to a just perceivable increment of pleasure, $dn$ to a sentient individual, $dt$ to an instant of time).
ibid. pp. 56–57