are said, by the great naturalist just quoted, to "labour at the decomposition of scorified matter." The mountain violets grow in abundance among the various lichens which encrust the ridges of the Cordilleras, and large hilly tracts of the island of Iceland, and wide plains of Lapland, are covered with a thick mass of the reindeer lichen, which gradually improves a soil on which, in spring and summer, arise thousands of blossoms, included in the simple name of reindeer flowers. Linnæus called the seaweed tribe vernaculi, or bond slaves, because they were fettered to the rocks on which they grew; but this name, as Burnet remarks, is still more appropriate to the lichen tribe, for they are chained to the soil, that they may benefit it, while they are not nourished by it. "And how," asks this writer, in a beautiful passage, of which we shall quote the whole, "how is their frail dust to maintain its station on the smooth and polished rock, when vitality has ceased to exert its influence, and the structure that fixed it has decayed?" This is a point which has been too generally overlooked, and yet which is the most wonderful provision of all. The plant when dying, digs for itself a grave, sculptures in the solid rock a sepulchre, in which its dust may rest; for chemistry informs us, that not only do these lichens consist in part of gummy matter, which causes their particles to stick together, but that they likewise form, when living, a consider able quantity of oxalic acid, which acid, when by their decay set free, acts upon the rock, and thus is a hollow formed in which the dead matter of the lichen is deposited. Furthermore, the acid, by combining with the limestone or other material of the rock, will often add an important mineral ingredient to the vegetable mould; and not only this, the moisture thus conveyed into the cracks and crevices of rocks and stones, when frozen, rends them, and by continued degradation adds more and more to the forming soil. Successive generations of the bond slaves successively and indefatigably perform their duties, until at length, as the result of their accumulated toil, the barren breakers or the pumice plains of a volcano become converted into fruitful fields."

There are persons, well-educated persons too, who if they marked the botanist in his earnest study of the grey shaggy

tree, would smile, almost contemptuously, on his labours. Yet facts like the one just adduced serve to show how sublime a lesson of God's glory may be obtained by examining even the humblest plants of the vegetable kingdom. Let us not forget the truth which the psalmist declared, "He hath made his wonderful works to be remembered;" and that the finite may learn something of the Infinite, from the blade of grass, or the drop of dew; from the little weed of the sea, or the grain of gold in the ore; from the thick green scum of the rivulet, or the ragged lichen of the rock; as surely as highest lessons of Omnipotence may be learned by looking on the sun and moon in their glory, and by the nightly glory of the starry skies.

There are, doubtless, a great number of species of the lichen tribe which have hitherto escaped the attention even of botanists. Unlike many other plants, the species are little varied in the different climates of the globe; thus the lichens of Europe and of North America are very similar. The numbers actually known, either in herbaria or books, has been estimated at 2,400.

If the lichen has less beauty of hue and less symmetry in form than either the ferns or mosses, or indeed, than any other order of cryptogamic plants, yet neither of the others can rival it in the direct service which individual lichens render to mankind, though the part which mosses perform in waste lands renders them, ultimately, so beneficial, as that we know not which of these two tribes is the more important. In those polar regions, where there is little trace of vegetation, save that of the moss and lichens, the inhabitants subsist for the greater part of the year on the plants of the latter, and often they form the only fuel. Sir John Franklin, when on the shores of the Polar Sea, observes that their fuel consisted chiefly of the roots of the decayed stunted pines, which gave them hardly enough heat for cooking. But there were places and seasons when and where even this could not be procured, and then the reindeer lichen, and other similar plants, which grew in profusion on the gravelly acclivities of the hills, were used as substitutes; and our distressed countrymen found that the burning lichens yielded more warmth than they had expected.

The Iceland moss, or as it is more cor

rectly called, the Iceland lichen, is not only a common article of Icelandic diet, but it is also largely exported both from that country and Norway, where it also grows abundantly. Large plains and hills of lava are, in Iceland, covered with this lichen, and it attains there a large size. Our own native mountains furnish it too in smaller size and less quantity; but much of the lichen is imported into our land from Norway, Lapland, and Sweden. We generally receive it before it has fully attained its growth, for it is collected while young, because those who gather it find it too valuable to leave it to grow to its full size. When in a dry state, it has scarcely any odour; but it has a bitter and unpleasant flavour. This is obviated by the mode of preparation, and the soup made from it in the lands of the north of Europe, is said to be twice as nutritious as that made of flour. Dr. Henderson observes of it: "For supper the Icelanders have either skyr, (coagulated milk,) or porridge made of Iceland moss. To a foreigner this is not only the most healthy, but the most palatable of all the articles of Icelandic diet." Three sorts of plants are said by Von Troil to be converted into bread by the Icelanders. This lichen, which they call fial, or rock grass; the kornsyra, which is the common polygonum of our meadows, called snake's weed, and the young shoots of which, familiarly known as the easter giant, are eaten in herb puddings in the north of England; and the melar, which is a species of reed. Several other kinds of lichen, besides that especially termed Iceland moss, are abundant in the island, and are also used as food.

These lichens are said to make, when ground into flour, a far better bread in flavour than the sour rye, hard kind of biscuit-bread imported from Copenhagen, or the tough doughy loaves of that city, made also from rye flour. The Icelander is, at any rate, satisfied with his humble meals; and when he gathers his lichen, and thanks the "God who has made bread to grow out of the very stones," we feel that he is at least blessed with that spirit of being content with such things as he has, which is a higher source of enjoyment than aught that worldly wealth or luxury could bestow.

Dr. Henderson gives an interesting account of the manner in which the simple-minded people of Iceland collect the lichen during the season in which it

grows most abundantly. The female portion of the family repair, about the middle of the summer, to gather the fiallagros, as they term the plant, in the uninhabited part of the island. They usually have one or two men to accompany them, and the few weeks which they spend in this rustic employment are among the happiest of the whole year. They fix their tents whereever the lichen is in greatest quantity, removing them from place to place as they clear each spot. During this season, the men of the Icelandic peasantry are either fishing in the fresh water streams, or proceeding in large parties to the factories, where they barter their home produce for articles of necessary use or comfort in the winter season. The tents in which the Icelandic women dwell during their country residence are, Dr. Henderson remarks, much like those of the Bedouin Arabs, and this nomadic life on the mountains is as delightful to them as even the wild free life which the Arab spends on his desert.

The Iceland moss contains a great quantity of starchy matter, of a highly nutritious quality, and it is imported hither, and much used for consumptive patients, its tonic qualities rendering it valuable as a medicine for those who have been greatly emaciated by long illness. It has also been extensively used in our land for ship biscuits, and the biscuits made of this powder have the advantage of remaining uninjured, either by sea water or insects, during long voyages. Those who do not know how to prepare the lichen rightly, cannot eat it, on account of its great bitterness; and this was the case with sir John Franklin and his party, when, to relieve the horrors of hunger, they were glad to subsist on the most wretched food. They boiled the Iceland moss which they collected from the rocks; but not having been previously soaked in water, its intensely bitter flavour prevented their being able to touch more than a few spoonfuls of it. The whole party must certainly have perished, however, had it not been for some species of the lichen, termed by botanists gyrophora. Several plants of this genus are included under the general name of trife de la roche, by which they are called by the Canadian hunters. When these lichens were frozen, the unfortunate travellers suffered dreadfully from the pangs of hunger. They ate raw and putrid flesh, and soup made

of bones so acrid, that unless when they had saved a quantity of the lichen to mingle with it, it often excoriated their mouths. Dr. Richardson speaks with joy of having one day found a bag-full of the trife de la roche. "It was easier," he says, "to gather this weed on a march than at the tent; for the exercise of walking produced a glow of heat which enabled us to withstand, for a time, the cold to which we were exposed in scrap ing the frozen surface of the rocks. On the contrary, when we left the fire, to collect it in the neighbourhood of the hut, we became chilled at once, and were obliged to return very quickly." Sometimes they were so happy as to find a less tasteless food, in a few blueberries and cranberries which the melting snows had laid bare, and now and then the crustaceous branched tufts of the lichen, called cornicularia, greeted their view; and being moistened and toasted over the fire, was truly a luxury. But the lichen soup became unpalatable by frequent use, and in some of their numbers it produced illness; and when they laid their worn and exhausted frames down for their nightly rest, the bright and vivid dreams brought to them pictures of costly viands and delicious banquets, and they woke up in the morning to the miseries of starvation, to endure the literal fulfilment of a Scripture prophecy against the enemies of the ancient Jews, "It shall be even as when a hungry man dreameth, and, behold, he eateth; but he awaketh, and his soul is empty: or as when a thirsty man dreameth, and, behold, he drinketh; but he awaketh, and, behold, he is faint, and his soul hath appetite," Isa. xxix. 8.

SUSPENSION BRIDGES.

A. P.

THE variations in the natural properties of bodies have given infinite scope for the exercise of human ingenuity. In the erection of engineering works, and in a still higher degree in the contrivance and construction of moving machinery, the combination of theory and practice is perpetually exhibited in surprising perfection. By nice calculation of the opposing forces, together with great practical skill in the mechanical details of construction, we can now attain a result in which abundant strength is united with the utmost possible economy of space and material. There is no waste; no addition of useless and cum

brous weight: all irregular strains are skilfully counterbalanced, and the greatest pressure distributed over the points of greatest resistance. Experience has entitled us to place implicit confidence in the scientific precision of our engineers. Every day we trust our lives and fortunes, without misgiving, into situations where a slight error in the calculations, or a slight defect in the workmanship, would inevitably lead to some terrible catastrophe. How little do the crowds who throng the deck of a Thames or Clyde steamboat, or, who allow themselves to be hurried along at fifty miles an hour in a railway carriage, reflect upon the delicate conditions which must have been fulfilled--the complicated mechanical problems which must have been solved, in order that they might accomplish their journey in security. A multitude will gather upon a suspension bridge without fear of danger, although the rods by which the massive roadway and its living freight are sustained appear as mere threads in comparison with the mass they have to support; while, if any one reflects at all upon the matter, it is to assure himself that every possible amount of pressure has been theoretically provided for; and that, practically, every separate bar and joint has been severely tested, so that no single flaw in the material, or defect in the workmanship can have passed without detection. Fribourg, before the civil war of the Sonderbund had given it a political notoriety, was celebrated chiefly for its wire bridge, hung at an altitude of nearly one hundred feet, between two summits." It looks," says a recent traveller, "like a spider's web flung across a chasm, its delicate tracery showing clear and distinct against the sky." Diligences and heavy wagons loomed dangerously as they passed along the gossamer fabric.

In works of similar construction to the Fribourg bridge, the limit of magnitude is, of course, found in that proportion where the erected mass is only just able to sustain its own unloaded weight without fracture. Practically testing the strength of the various metals, we find that a regularly shaped bar or column of steel, if suspended perpendicularly by its upper extremity, will be torn asunder by its own weight at a length of 44,350 feet. Iron would break at about 25,000; copper at 9,500; gold at 2,880; and lead at only 180 feet. The processes of annealing and wiredrawing will modify, to a