He reflects on the accumulation of the mountain-snows, each year adding fifty-eight inches of ice to a glacier. This would make Mont Blanc four hundred feet higher in a century, and four thousand feet higher in a thousand years. "It is evident," he says, "that nothing like this occurs in nature." The escape of the ice then leads him to make some general remarks on what he calls the "law of circulation." "The conserving will of the Creator has employed for the permanence of His work the great law of _circulation_, which, strictly examined, is found to reproduce itself in all parts of nature. The waters circulate from the ocean to the air, from the air to the earth, and from the earth to the ocean.... The elements of organic substances circulate, passing from the solid to the liquid or aeriform condition, and thence again to the state of solidity or of organisation. That universal agent which we designate by the names of fire, light, electricity, and magnetism, has probably also a _circulation_ as wide as the universe." The italics here are Rendu's own. This was published in 1841, but written, we are informed, nearly two years before. In 1842 Mr. Grove wrote thus:--"Light, heat, magnetism, motion, and chemical affinity, are all convertible material affections." More recently Helmholtz, speaking of the "circuit" formed by "heat, light, electricity, magnetism, and chemical affinity," writes thus:--"Starting from each of these different manifestations of natural forces, we can set every other in action." I quote these passages because they refer to the same agents as those named by M. Rendu, and to which he ascribes "_circulation_." Can it be doubted that this Savoyard priest had a premonition of the Conservation of Force? I do not want to lay more stress than it deserves upon a conjecture of this kind; but its harmony with an essay remarkable for its originality gives it a significance which, if isolated, it might not possess. [Sidenote: GLACIERS RIGHTLY DIVIDED.] With regard to the glaciers, Rendu commences by dividing them into two kinds, or rather the selfsame glacier into two parts, one of which he calls the "_glacier reservoir_," the other the "_glacier d'ecoulement_,"--two terms highly suggestive of the physical relationship of the _neve_ and the glacier proper. He feeds the reservoirs from three sources, the principal one of which is the snow, to which he adds the rain, and the vapours which are condensed upon the heights without passing into the state of either rain or snow. The conversion of the snow into ice he supposes to be effected by four different causes, the most efficacious of which is _pressure_.[B] It is needless to remark that this quite agrees with the views now generally entertained.