Selected Miscellany.

Dr. Turner, of New York, who has made the geology of the Sierra Nevada a long-time study, has published a monograph in which he asserts, with plausible reasoning, that the many kinds of rocks characterizing that formation have been formed in part by deposition beneath the sea, and in part by intrusion as igneous masses, also by eruption from volcanoes, and portions of them have been subsequently metamorphosed. While the southern portion of the range is composed of granite, he finds that the central and northern part, west of longitude 120 degrees, consists prevailingly of schists, these having been produced by intense metamorphism of both ancient sediments and igneous rocks, and it is in these schists, chiefly though not solely, that the auriferous quartz veins occur. Further, the trend of the bonds of altered sediments and of other schistos structure is generally from northwest to southeast, parallel to the trend of the range, but great masses of granite and other igneous rocks have been intruded among the schists, forming irregular bodies which interrupt the regular structure and which are generally bordered each by a zone of greater metamorphism. These schists, with their associated igneous masses, form the older of the two great groups of rocks, recognized in the Sierra Nevada.

WEATHERING OF BUILDING STONES.

The artificial testing of endurance of building stones exposed to the atmosphere by means of the formation of crystals of some suitable substance in their pores has for many years come to be regarded as satisfactory, although it raises the question which we pointed out in our former comments on this subject whether the artificial procedure can be considered equivalent to the natural process of weathering. It is almost certainly not exactly equivalent, but we think it is a question well worth considering whether it is even approximately so. No theoretical considerations are sufficient for the determination of the physical forces developed or the changes produced in the material by them.

It is not impossible that small chemical reactions, at least, may take place in the material of some stones when treated by the sulphate of soda or similar processes, although it is improbable that such effects often result to an appreciable extent. Leaving out of account, however, all such influences, there still remains the fact that the destructive effects produced by the formation of ice in the small interstcies (sic) of stone are almost certainly not identical with those induced by the formation of the crystals of such chemical substances as sulphate of soda.

It may, of course, be said that, while considerable inequality in these results may exist, yet the destructive effects of artificial crystallization may furnish a basis for a comparative or quantitative inference in regard to the weathering capacity of any given material. This is probably true, and the observations would possess practical value were there in existence actual data establishing probable relative capacities among a given set of stones.

Again, there is a class of weathering effects due to the action of the sun, and resulting from alternate expansions and contractions, to say nothing of slow possible chemical actions, of which no artificial process of crystallization can give us any measure. It is seen, therefore, that the latter class of tests fail in some very material characteristics of furnishing to the engineer such a measure of weathering endurance as he should desire or demand.

We do not make these observations in the line of hypercriticism, because we recognize the fact that the engineer, like everyone else, must always use the best means at his command to accomplish any desired end, although these means may fall very short of meeting the conditions which he fully recognizes. Mr. Luquer's admirable paper, read before the American Society of Civil Engineers, shows conclusively what has been at least partially recognized before-viz., that the sulphate of soda process is much more severe in its effects on the considerable number of stones which he tested than the same number of alternate freezings and thawings, and to an extent which varies widely with stones of different texture. While, therefore, the sulphate of soda and similar processes may and do give valuable information to the engineer in regard to certain weathering properties, and while such tests must necessarily in some cases be the only endurance tests available, their results should in all possible cases be supplemented by the effects actual weathering exposure wherever possible. Indeed, it is probable that there is no better measure or resistance to weathering by building stones when available than that exhibited by the outcrop of the quarries which have been exposed to all weathers and all seasons through perhaps centuries of time. On account of the varying qualities of stone in the same quarry this test is obviously unusually unavailable, but engineers with a very little forethought and trouble may accumulate in the course of a few years data in regard to the weathering properties of natural and artificial stone of a most valuable character by submitting specimens to continuous exposure under such conditions as will develop effects of sun, frost, and other influences which act on the exposed faces of buildings.

ROMAN VAULTING.

Want of wood for scaffolding might be the cause why vaulting was so much disregarded by the Egyptians and Greeks. As to the Romans, they, says Wincklemann taking advantage of the solidity which the pouzzolane (a particular sand) acquires in a short time, used more cement than stone in vaulting. When the frame was covered with carreaux or planks they threw over cement, very small stones, or bruised bricks, to ascertain thickness (5 feet 4 inches in the Thermæ of Dioclesian). By this means a few men could build a large vault in a day. This construction appears at the Coliseum, the Baths of Titus, Caracalla, and Dioclesian, and particularly at Adrian's Villa, where are still seen the beds of the planks of the frame. As the ancients made their vaults very strong they endeavored to render them as light as possible. This they did by two methods.

One was to fill the vaults with volcanic Scoriæ, some of which have been found at the Pantheon. The other consisted in using urus or vases of terra cotta, the apertures being placed at top. Within and around them they poured small stones and cement. Denon thus describes arches of this construction which he found at Vianisi, in Sicily. A sort of phials, 8 inches long by 3 inches wide, without bottoms, and filled with mortar, have their necks introduced into each other in a row, covered over again with a general coat of plaster on which a brick was laid flat, then a fresh bed of mortar and another brick upon this, like the former. It was scarcely possible ever to destroy semicircular arches fabricated in this manner, and it was with the utmost difficulty that Denon wrenched off a few fragments. Alberti says that this construction of phials was used on purpose to ease the weight, and that they had no bottoms lest water should collect in them, and so render them heavy. But this construction must not be confounded with vases used on purpose to augment the sound. Evelyn saw a room covered with a noble cupola, built purposely for music, the fillings up or cove between the walls, being of urns and earthen pots for the better sounding.

ENGINEERING TOOLS AT POMPEII.

Under the title of "Things of Engineering Interest Found at Pompeii," Professor Goodman lately gave his inaugural lecture in the engineering department of the Yorkshire College, Leeds. The lecturer remarked that he had recently visited Pompeii, and was not only charmed by the great beauty of the works of the ancient Romans, but also by their extreme ingenuity as mechanics-in fact, it was a marvel how some of the instruments and tools they were in the habit of using could possibly have been made without such machinery as we now possess. After explaining the situation and destruction of Pompeii by showers of ashes and mud, not lava, as is usually supposed, in the year 79 A. D., Professor Goodman showed a series of about fifty lantern slides, prepared from photographs taken by himself in Pompeii last Easter. The streets he explained, were used as waterways to carry off the surface water, and probably sewage from the houses. The pavements were raised about a foot above the streets, and stepping stones were provided at intervals for foot passengers. The horses and chariot wheels had to pass between, and in many places deep ruts have been worn by the chariot wheels in the stone paved streets. The water supply of Pompeii was distributed by means of lead pipes laid under the streets. There were many public drinking fountains, and most of the large houses were provided with fountains, many of most beautiful design. The amphitheater, although a fine structure, capable of seating 15,500 people, was small compared with many in Italy. The bronzes found at Pompeii reveal great skill and artistic talent. The bronze brazier and kitchener were provided with boilers at the side and taps for running off the hot water. Ewers and urns have been discovered with internal tubes and furnaces precisely similar to the arrangement now used in modern steam boilers. Several very strong metal safes, provided with substantial locks, have been found. The locks and keys were most ingenious, and some very complex. On looking at the iron tools found in Pompeii, one could almost imagine he was gazing into a modern tool shop, except for the fact that the ancient representatives have suffered severely from rust. Sickles, billhooks, rakes, forks, axes, spades, blacksmiths' tongs, hammers, soldering irons, planes, shovels, etc., are remarkably like those used to-day; but certainly the most marvelous instruments found are the surgical instruments, beautifully executed, and of design exactly similar to some recently patented and reinvented. Incredible as it may appear, yet it is a fact, that the Pompeiians had wire ropes of perfect construction.

THE PORTABLE ENGINE.

by W. D. Wansbrough

The portable steam engine, or, to use the convenient continental expression, the "locomobile," is one of the most widespread and familiar products of British industry, and may, indeed, nowadays almost claim the honorable distinction, hitherto universally accorded to its big brother, the locomotive can wake the echoes of the primeval forest with its mighty roar, you may be sure that the tiny shriek of the portable engine-sawing, grinding, pumping or what not-has been heard in the land. These engines are the drudges of the engineering word-mechanical children of Gibeon-hewers of wood and drawers of water.

Rough treatment and unskilled attendance are the common lot of the portable engine, and it may, at first sight, seem that its purpose would be answered by a combination of the simplest and most rudimentary form of steam engine with the cheapest possible boiler. And when it is further remembered that in all probability, of all productions of human brains and fingers, you get more value for money in a portable engine than in any other article that it is possible to purchase, the arguments in favor of a strong, clumsy and roughly finished machine, as the most likely to fulfill the conditions, would seem to be conclusive.

The direct contrary, however, is the fact. A specimen may be selected at random from almost any maker, large or small, and you will find in the ordinary, everyday commercial portable engine an example of careful and intelligent design, liberal proportions and good workmanship, which might be followed with advantage by makers of much more pretentious machinery. As a natural result, the demand has been enormous, and this, in turn, has led, in the cases of the leading makers, to an extraordinary development of their manufacturing appliances. The portable engine industry has, indeed, assumed very large proportions in Lincolnshire and the eastern counties of England, but for some inexplicable reason, attempts to introduce the manufacture into other parts of the country have rarely met with success.

- W. D. Wansbrough, in Cassier's Magazine for December.

[Top of Page]