236. The following experiments, by Mr. Buchanan, on the stiffness of bars of Memel fir and of cast-iron are important. The specimens were supported at the ends and loaded in the middle; and the effect of a successive increase of weight is shown.

237. In carpenters' work it is obvious that a long beam may have a greater degree of bending than a short one, and yet be as fit for its purpose; hence, if we allow the quantity of bending of a beam in its place to be proportional to its length, the absolute stiffness being as the cube of the length, the comparative stiffness will be as the square of the length; and the last column in each of the preceding Tables shows the stiffness of a bar one foot long and one inch square, from whence that of any other sized beam may be obtained by proportion, as follows:

As the square of the length, in feet,

Is to the weight supported by the inch bar, one foot long,

So is the breadth multiplied into the cube of the depth

To the weight the beam should support.

238. In this proportion, the load or weight is supposed to be applied in the middle; but, if it be distributed regularly over the beam, eight-fifths of the weight found by the proportion would be sustained with an equal degree of bending.

EXAMPLES.

239. Example 1.-Required the weight a beam of Memel fir will support in the middle, without bending more than one-fortieth of an inch for each foot in length, its length being 10 feet, and its depth 9 inches, and breadth 44 inches.

The square of the length is 10 x 10=100;

The cube of the depth multiplied into the breadth is 9 × 9 × 9 × 4=3282};

And, by the table, the weight supported by an inch bar, is 66 lbs.

Therefore, 100 : 66 :: 3282 2166 lbs. the Answer.

66

19695

19695

1,00) 2166,45 (

If the weight had been to be uniformly distributed over the length, then it should have been divided by 5, and multiplied by 8; thus,

5)2166
433
8

3464 lbs.-the weight that might be distributed.

240. Example 2.-If the distance between the supports of a bressummer of Memel fir be 12 feet, and that five-eighths of the weight of the wall and floors it has to support be found to be 9600 lbs., and its breadth 14 inches, it is required to find its depth, so that the bending may not exceed the quantity stated in the rule.

The cube root of 1496 is nearly 114 inches, the depth required.

These examples will, perhaps, be sufficient to direct the reader how to apply the rules to some of the most important cases in practice; but, if he wishes for further information, he will find various examples and tables ready calculated in Tredgold's Elementary Principles of Carpentry.

For the ordinary purposes of building, it is not necessary to calculate the bending of beams of cast-iron, provided they be not loaded with more than one-fourth of the breaking weight; but it may be useful to know, that the rule for strength will produce the same result as the rule for stiffness, when the length of a cast-iron beam in feet, is four-thirds of the depth in inches; and this is a very good proportion for the depth. If the depth be less than in this proportion, a cast-iron beam will bend more than half an inch in a length of 20 feet; and, if the depth be greater, it will bend less, and must have its proportions fixed by the rules for strength.

In oak and fir, the reverse happens; for, unless the depth in inches be about double the length in feet, the bending is always greater than the proportion assigned in the rules for the stiffness of beams.

CARPENTRY, JOINERY, &c.

BOOK II.

JOINERY.

CHAPTER I.

1. JOINERY

INTRODUCTION.

OINERY is the art of uniting and framing wood, for the internal and external finishing of buildings. In Joinery, therefore, it is requisite that all the parts should be much more nicely adjusted to each other than in Carpentry, and all the surfaces which are to be exhibited to the eye should be made perfectly smooth.

2. In early times, says the author of an article on this subject in the Encyclopædia Britannica, very little that resembles modern joinery was known; every part was rude, and joined in the most artless manner. The first dawnings of the art appeared in the thrones, stalls, pulpits, and screens, of our Gothic cathedrals and churches; and even in these, it is of the most simple kind, and is indebted to the carving for every thing that is worthy of regard. Whether, in these ages, the carver and the joiner had been one and the same person, we cannot now determine, though we imagine, from the mode of joining in some of them, that this was the

case.

During several centuries joinery seems to have been gradually improving, but nothing appears to have been written on the art before 1677, when Mr. Joseph Moxon, a Fellow of the Royal Society, published a work, entitled 'Mechanic Exercises, or the Doctrine of Handy-works.' In this work the tools and common operations in joinery are described, with a collection of the terms then in use. It must have been a valuable work at that time, but to one who could previously work in the art it would convey little, if any thing, that was new. Sash-windows were introduced into England some time before the date of Moxon's work, but he has not noticed them. According to the observations of Dr. Thomson, this important improvement has not yet found its way into Sweden.-(Travels in Sweden, p. 8.)

About the beginning of the last century, several works on Joinery, of a most interesting description, made their appearance; and forms began to be introduced in architecture, which could not be executed at a moderate expense without the aid of new principles, and these prin

Y

ciples were discovered and published by practical joiners. As might naturally be expected, these authors had but confused notions, owing chiefly to their want of sufficient geometrical knowledge; and, accordingly, their methods are often obscurely described, and they are sometimes quite erroneous.

The hand-rails of stairs offered many difficulties, and an imperfect attempt to remove them was first made by William Halfpenny, in his Art of Sound Building, which was published in 1725. Francis Price, the author of the British Carpenter, published in 1733, was more successful, and his remarks show a considerable degree of knowledge of the true nature and object of his researches. The publication of Price's work, of which we have seen five editions, must have produced a considerable sensation among the joiners of that period, for it was soon followed by many other works of different degrees of merit. Of these, the works of Batty Langley, and Pain's works, were the most popular.

The establishment of the principles of Joinery in this country, on the sound basis of geometrical science, was, however, reserved for Nicholson. In his Carpenter's Guide, and Carpenter's and Joiner's Assistant, published in 1792, he made some most valuable corrections and additions to the labours of his predecessors.

3. Corresponding improvements were also made in the practice of joinery, for which we are much indebted to the late Mr. James Wyatt, and the other branches of his family. That celebrated architect kept together some of the best workmen in London, and these were looked up to with a degree of emulation, by young men, which had a most beneficial effect on the progress of joinery. But the art is still far short of perfection. We conceive that many of those operations, on which the soundness of work chiefly depends, might be done with greater exactness, and less labour, by improving the tools used for these purposes, or by the invention of new methods of performing such operations.

4. The true geometrical principles of joinery were published in France at a much earlier period than in England, and by a very different class of writers. The extensive work of Frezier, entitled Coupé des Pierres et des Bois, in 3 vols. 4to. 1739, contains all the leading principles of the art, and explained with tedious minuteness; offering a striking contrast to the brevity of our English authors. The first elementary work on that part of geometrical science, which contains the principles of joinery, appeared in France, in 1795, from the pen of the celebrated Gaspard Monge, who gave it the name of Géometrie Descriptive. Much of what has been given as new in English works, had been long known on the Continent; but there does not appear to have been much, if any, assistance derived from these foreign works by any writer prior to Nicholson.

Rondelet's Treatise on the Art of Building, (L'Art de Bâtir,) published in 1814, contains a very good treatise on Joinery; but the latest French work we have seen on the subject is that of Krafft, published in 1820, in large folio, and in three languages. The English part very imperfect, and the whole work full of pretension which it never realizes. Rondelet's is decidedly the best French work on the subject we have seen; but it is not at all adapted to the state of joinery in England. In practice, the French joiners are very much inferior to our own. Their work is rough, slovenly, and often clumsy; and, at the best, is confined to external effect. The neatness, soundness, and accuracy, which are common to every part of the works of an English joiner, are scarcely to be found in any part of the works of a French one. The little correspondence, in point of excellence, between their theory and practice, leads us to think that their theoretical knowledge is confined to architects and engineers, instead of being diffused among workmen as it is in this country.