M. Rendu, Bishop of Annecy, to whose writings I have just referred, died last autumn.[A] He was a man of great repute in his diocese, and we owe to him one of the most remarkable essays upon glaciers that have ever appeared. His knowledge was extensive, his reasoning close and accurate, and his faculty of observation extraordinary. With these were associated that intuitive power, that presentiment concerning things as yet untouched by experiment, which belong only to the higher class of minds. Throughout his essay a constant effort after quantitative accuracy reveals itself. He collects observations, makes experiments, and tries to obtain numerical results; always taking care, however, so to state his premises and qualify his conclusions that nobody shall be led to ascribe to his numbers a greater accuracy than they merit. It is impossible to read his work, and not feel that he was a man of essentially truthful mind, and that science missed an ornament when he was appropriated by the Church.

The essay above referred to is printed in the tenth volume of the Memoirs of the Royal Academy of Sciences of Savoy, published in 1841, and is entitled, 'Théorie des Glaciers de la Savoie, par M. le Chanoine Rendu, Chevalier du Mérite Civil et Secrétaire perpétuel.' The paper had been written for nearly two years, and might have remained unprinted, had not another publication on the same subject called it forth.

I will place a few of the leading points of this remarkable production before the reader; commencing with a generalization which is highly suggestive of the character of the author's mind.

"THEORIE DES GLACIERS DE LA SAVOIE."

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 aëriform 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.

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 réservoir," the other the "glacier d'écoulement,"—two terms highly suggestive of the physical relationship of the névé 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.

In page 60 of the volume referred to there is a passage which shows that the "veined structure" of the glacier had not escaped him, though it would seem that he ascribed it to stratification. "When," he writes, "we perceive the profile of a glacier on the walls of a crevasse, we see different layers distinct in colour, but more particularly in density; some seem to have the hardness, as they have the greenish colour, of glass; others preserve the whiteness and porosity of the snow." There is also a very close resemblance between his views of the influence of "time and cohesion" and those of Prof. Forbes. "We may conclude," he writes, "that time, favouring the action of affinity, and the pressure of the layers one upon the other, causes the little crystals of which snow is composed to approach each other, bring them into contact, and convert them into ice."[C] Regelation also appears to have attracted his notice.[D] "When we fill an ice-house," he writes, "we break the ice into very small fragments; afterwards we wet it with water 8 or 10 degrees above zero (Cent.) in temperature; but, notwithstanding this, the whole is converted into a compact mass of ice." He moreover maintains, in almost the same language as Prof. Forbes,[E] the opinion, that ice has always an inner temperature lower than zero (Cent.). He believed this to be a property "inherent to ice." "Never," he says, "can a calorific ray pass the first surface of ice to raise the temperature of the interior."[F]

OBSERVATIONS AND HYPOTHESES.

He notices the direction of the glacier as influencing the wasting of its ridges by the sun's heat; ascribing to it the effect to which I have referred in explaining the wave-like forms upon the surface of the Mer de Glace. His explanation of the Moulins, too, though insufficient, assigns a true cause, and is an excellent specimen of physical reasoning.