a waterwheel or other power; the makers of the Taylor compressor, however, claim a good efficiency for their apparatus, and, as has been seen, the pressure obtained may be made as great as desired by making the shaft sufficiently deep. Some of its apparent advantages, as a method of utilizing a fall of water for producing a supply of compressed air, are its simplicity of construction, which

should make the cost of operation and maintenance small, and the fact that the air, while being compressed, is in such close contact with water that the heat developed during its compression is at once absorbed by the water, thus allowing the compression to take place at a practically constant temperature, and reducing, to a considerable extent, the work required to compress a given quantity of air.

LA

AST month we spoke of mechanical drawing as a language, and discussed what we called its alphabet. A projection line was shown to be an imaginary line passing through, and at right angles to, an imaginary plane, situated between the eye and an observed body. We shall presently discover the true value of the projection line in mechanical drawing.

The following riddle is often asked and as often puzzles the victim : "What is the shape of the body that will fit either a round, square, or triangular hole?" On the spur of the moment one is rather inclined to say that such a body is impossible. A proper use of the language of

HOME STUDY,

FIG. 1.

mechanical drawing, however, will enable us to solve the riddle. The body must fit either a round, square, or triangular hole; construct, then, a circle, a square, and a triangle; arrange them as in Fig. 1, and what do we learn? We learn that a body whose plan is a circle, whose side view is a square, and whose end view is a triangle, fulfils all the conditions. What does such a body look like? Fig. 2 is a perspective drawing of it, and Fig. 3 shows that the projections of it

* Begun in the May Number.

are precisely similar to those shown in Fig. 1. Here we have an example of a very simple body, which it would be difficult to represent to the patternmaker or machinist without the aid of a mechanical drawing. Three views of it are necessary, in order to show that the plan is circular, the side view square, and the end view triangular.

Now let us deal with the casting shown in Fig. 4. This representation of it would be of no use in the pattern shop; it would be impossible, even with the aid of a written description, to make it of real practical use. The mechanical drawing, however, of Fig. 5 tells the whole story without the aid of either verbal or written explanation. To make clear the meaning of each view of this mechanical drawing, we will deal with the casting much as we did with the prism last month; in other words, we will place it behind transparent planes, and view it from the positions indicated by the groups of eyes in Fig 6. We make use, as before, of the three plates X, Y, and Z, but, in order to look straight at the inclined side of the casting, we introduce a fourth plate W, which we make parallel to the inclined side, and at right angles to the top plate X. There is probably no need to explain the reason for doing this. If you want to see the shape of anything you naturally stand in front of it.

HOME STUDY. FIG. 2.

Now, if the plates Y, ', and Z are swung up about their hinges, we get what is shown in Fig. 7; and this is precisely what we

already know to be a mechanical drawing of the casting.

Remembering that the views as drawn on the plates X, Y, Z, and W are projections of the shape of the casting as viewed from immediately in front of the respective plates, and that the imaginary lines from the eye, in its various positions, to the casting are projection lines, we find that the mechanical drawing is simply a plan of the views in Fig. 6 after they are swung up into the horizontal, as shown in Fig. 7, and that the

simplified. We have first the prism itself, then the actual projections of it upon the

projection lines of Fig. 6 become, in plan, as shown in Fig. 5. A good machine designer never forgets this, nor does he ever lose sight of the solidarity of the object he is representing. If he is designing a casting, such, for instance, as that shown in Fig. 4, he first forms a mental picture of the general proportions of the completed piece, not trusting to making important discoveries as he goes along, but leaving only the details to be worked out in the actual drawing. In this way he makes intelligent use of projection lines, and is free to interpose any number of imaginary planes, such as Win

No

OT long since a New York paper offered a prize for the solution of the following puzzle: "How many pieces can be made by dividing a pie with seven straight cuts of a knife?"

At a first glance the puzzle seems a hard one to answer, but a little thought will show that to get the maximum number of pieces, one needs but to observe the following rule:

Be sure that each successive cut crosses every previous one and at some point that is not the intersection of two previous cuts.

It will then be found that seven straight

OST of our readers are probably familiar with the "big trees of California❞— the Sequoia gigantia. Many, doubtless, have seen them, and stood in awe before these giants of creation. Few, however, have seen or even thought of them as sometimes turned into stone. Last summer in a little park called Florissant, 9,000 feet above the sea and in the heart of the Colorado range of mountains, we came across half a dozen stumps of these trees, from ten to fifteen feet in diameter, all of them within a square acre, and all turned into solid, hard stone. One stump in particular had been partially excavated from its bed by some enterprising parties, with a view to carrying it to the World's fair. It stood twenty feet upright and was fifteen feet in diameter. As they could not carry it away bodily, they tried to saw it up in sections; but, fortunately for Colorado, the hard quartz composing it was more than a match for their stone saws, and the saws are still sticking in the tree as monuments to man's discomfiture.

So wonderfully had the stony material replaced the texture and grain of the original tree, and, in some parts, even simulated its reddish color, that, but for its unusual size, any one might have passed it by as an old dead pine stump, felled by some early settler. A Californian, however, would at once have recognized it, by the peculiar appearance and texture of the wood, as a fossil representative of his native redwood. Not only is the rough texture of portions of the thick bark preserved, but even the minute wood cells and annual rings of growth are retained. Here and there a little oxide of iron gives it somewhat the red tinge of the modern redwood, but the prevailing color is an ashen grey, like that of any old dead stump. As you pick up chips, scattered around by the hammers of tourists, their weight and hardness alone convince you that they are really stone and not pine chips left by the axe of an old-time woodsman. To complete the illusion and resemblance to the living tree, sap vessels and veins are here and there filled with what appears to be gum, but

what, on examination, proves to be as hard as glass, and consists of opal and chalcedony. Still more wonderful is it when we cut thin sections of the tree and put them under the microscope. We see the minute pattern of the wood cells, which vary in different living trees, and are often most intricate and beautiful in form, faithfully and microscopically replaced by stone; and, by comparing the peculiar pattern with that of sections of the living Sequoia, we find them identical, showing that this stone tree, more than a thousand miles from any living trees of its kind, which are only to be found on the Pacific coast, is, or rather once was, a genuine Sequoia, or big redwood tree.

The question arises, how was this tree so wonderfully changed into stone, and how did it find its way almost alone to the top of the Rockies?

Stone it certainly is; moreover, there is not a particle of the original tree in it, any more than there is flesh and blood in a marble statue or a plaster cast.

It is a not uncommon idea with some people that after death certain living substances or bodies have a mysterious power of turning themselves into stone. Such is not the case. Let an animal die on the prairie, and its flesh rots and passes away. Its skeleton may last a few years longer, but, if it could lie there, preserved, for a thousand years, there is nothing inherent in it that of itself could petrify it, or turn it into stone. So it is when a tree falls to the ground; it rots and becomes soil for other trees to grow on; the tree has no element in itself which is capable of transforming it into stone, still less without diminution of size.

Suppose a tree, like our Sequoia, to grow near a marsh or lake; the waters of the lake in time encroach on its roots and rot or kill the tree, burying the lower portion in mud. The upper part decays and falls into the water, becomes waterlogged, sinks to the bottom, and is entombed in mud, which, by preventing the access of air or water, prevents rapid decay.

In this condition petrifaction may begin. All waters carry a certain amount of minute mineral particles in solution; some contain iron, others soda or lime; and, if the waters are acid and heated-as they are apt to be when near volcanic sources— quartz or silica is contained in them, which is deposited as a gelatinous substance, like gum arabic, which afterwards hardens into stone. Our tree then, on the bed of the lake, is saturated with such mineral-bearing waters; the large open sap veins of the tree are quickly filled with solutions of quartz, forming agate, opal, or chalcedony. Then a wonderful microscopic work follows: As each minute particle and wood cell rots away, it is replaced by a particle of stony matter, until, when the entire living substance of the tree has passed away, a perfect restoration in stone of the tree that lived and perished ages ago is left behind as a monument for all time. Of course, this does not happen to every tree that falls into lake or river; certain waters and circumstances are more favorable than others. Particularly favorable, however, are the waters near a volcanic vent, where hot springs and acid gases abound to dissolve the silica.

The surroundings of this fossil tree are no less interesting than that of the tree itself. The roots are imbedded in shale and sandstone-the solidified mud of a primeval lake. On examining this we find that it is composed of grains and fragments of volcanic lava, sometimes as fine as the finest dust. Opening the leaves of these thin layers of mud with a knife, we found quantities of impressions of insects, such as ants, dragon flies, tropical lanthorn flies, and among them a solitary butterfly, the impression even retaining the pattern of the colors on the wings. Mingled with these were equally perfect impressions of fossil leaves of a semitropical character, such as the fronds of palmettoes. The fossil remains of a sparrow and numerous fossil fresh-water fish have also been found, all indicating a semitropical character for the age. From these remains and other data we gain a history of the lake and its contents.

Some thousands of years before the creation of man, a small lake nestled among these hills, its banks surrounded by a luxuriant semitropical foliage, among which, close to the edge of the lake, towered the great Sequoias.

In the near vicinity, volcanic eruptions took place, and by their violent explosions filled the air with clouds of dust and ashes, which

fell, from time to time, in showers into the lake to form its mud; leaves of trees that had been blown into the lake, insects and other living things, water-logged stumps of trees and many forms of vegetation were deeply buried beneath the volcanic mud. Here the hot and acid springs assisted in a fossilizing process. Finally, the eruptions ceased, the lake dried up; floods and glaciers cut ravines in the fossil rock, exposed the petrified stumps, and laid the beds with their fossil treasures open to the chisel of the explorer.

The Sequoias are probably the oldest as well as the biggest trees on this planet-survivals of an age long past-and when we stand gazing at their colossal forms in California we may truly say:

"This was the forest primeval," for they were among the earliest genuine trees to appear on this planet at all like those of the present age. Before them there were no forms that we would have recognized as true trees. The earliest forms of plant life or, if you like, tree life-were seaweeds, growing in a world of waters, a world of an almost universal ocean. Later, upon low islands just above sea level, were forms not unlike the grotesque seaweeds of the ocean, and later still, gigantic weeds and mosses, rushes and ferns-prodigiously magnified swamp vegetation-but still no genuine trees. Not until the middle of the earth's history, when those strange, gigantic lizards came upon the earth, did there appear the first true forest tree, and this was the great Sequoia. But this tree saw the age of lizards and reptiles fade away and give place to that of almost equally gigantic mammals. Later, it saw that marvel of creation, the first man ; and its son is with us today, and has seen the railroad train fly through its forest, and the telegraph wire pinned against its bark. In the present age there are but two varieties of the Sequoia known, and they are confined to the little border of the Pacific coast. In ancient times there were twentysix varieties, which were scattered over the world from the extreme Arctic circle to Australia. This accounts for our finding their fossil remains in Colorado. In all these regions, yes, even under the eternal snows of the Arctic circle in Spitzbergen, Melville Island, and Greenland, similar fossil remains have been found. Nay, more, some of our most eminent botanists and geologists think that the Arctic circle was the paradise of trees, from where they spread south over the globe.