A possible indication that there is no real mass in de~Sitter's world is afforded by a calculation of the gravitational flux~\Eq{(63.4)}. By~\Eq{(63.6)} this is \[ 4\pi r^{2} \left(-\delta y - \frac{2}{r}\, \delta\gamma\right) dt, \] since $dt$~can no longer be replaced by~$ds$. On substituting for~$\gamma$ it is found that the flux vanishes for all values of~$r$. It is true that as we approach the boundary $dt/ds$~becomes very great, but the complete absence of flux right up to the boundary seems inconsistent with the existence of a genuine mass-horizon. I believe then that the mass-horizon is merely an illusion of the observer at the origin, and that it continually recedes as we move towards it. \Section{71.}{Properties of Einstein's cylindrical world} \index{Einstein's cylindrical world}% Einstein does not regard the relation~\Eq{(69.5)} \[ M = \tfrac{1}{2}\pi R = \tfrac{1}{2}\pi \lambda^{-\frac{1}{2}} \Tag{(71.1)} \] as merely referring to the limiting case when the amount of matter in the world happens to be sufficient to make the form cylindrical. He considers it to be a necessary relation between $\lambda$ and~$M$; so that the constant~$\lambda$ occurring in the law of gravitation is a function of the total mass of matter in the world, and the volume of space is conditioned by the amount of matter contained in it. The question at once arises, By what mechanism can the value of~$\lambda$ be adjusted to correspond with~$M$? The creation of a new stellar system in a distant part of the world would have to propagate to us, not merely a gravitational field, but a modification of the law of gravitation itself. We cannot trace the propagation of any such influence, and the dependence of~$\lambda$ upon distant masses looks like sheer action at a distance. \PageSep{167}