Introduction to the mechanical principles of carpentry

When the Trustees of the Gardiner Lyceum had determined, a year or two since, to add to the regular classes, admitted annually, several winter classes to continue for a few months, for the benefit of those young men, whose circumstances would not permit them to devote any considerable time to study; it devolved upon the Author of the following pages to mark out, for each of these Classes, a course of study, which would be appropriate and not too extensive for the time allotted to them.

It was while fixing upon a course for the winter doss in Carpentry and Civil Architecture, that, the design of publishing this book suggested itself to him. He could find "books of lines" sufficient; was at no loss for exemplars of the orders; could easily provide for instruction in practical geometry and drawing; but knew of no book which appeared to him suited to instruct young men, who had made no advances in mathematics, beyond arithmetic and the simplest elements of practical geometry, in Carpentry, as " a branch of mechanical science."

"The many volumes," as Dr. Robison justly observes, "called Complete Instructers, Manuals, Jewells, &c. take a humbler flight, and content themselves with instructing the mere workman, and sometimes give the master builder a few approved forms roofs and other framings, with the rules for drawing them on paper, and from thence forming working draughts, which must guide the Saw and the chisel of the workman. Hardly any of them offer any thing that can be called a principle, applicable to many particular cases, with rules for their adaptation." Dr. Robison's own excellent articles, Carpentry, Strength of Materials, Roofs, &c. first published in the supplement to the Encyclopedia Brittannica, and afterwards in the first volume of his System of Mechanical Philosophy, have done much to supply the deficiency, of which he speaks in the passage just quoted, and which, in other places, he censures more explicitly and severely. Since the publication of Dr. Robison's articles, Mr. Tredgold has published, in London, his "Elementary Principles of Carpentry," which has justly been characterized as a work of great practical utility.

It may be thought, that Mr. Tredgold's work might supersede the necessity of the eye now offered to the public. To the Author it appeared otherwise. Mr. Tredgold's work is replete with the sound and judicious observations of a man, in whom practical knowledge is united with science; but it is not well constructed for elementary instruction. It frequently supposes the reader to be acquainted with the higher mathematics and mechanics, and a considerable part of it is taken up with the subject of Bridges, which adds to the expense of the work, and is not, to most carpenters, a matter of immediate interest.

The plan of this Introduction is, to give, in the first place, some knowledge of the Strength and Stiffness of Timber, as the foundation, both of the science and art of Carpentry. In this part of the work, the principles are deduced directly from a comparison of well conducted experiments; a method,- which, while it is the most satisfactory to practical men, and the only intelligible one to those, who are not skilled in mathematics, is also the most safe. This part is followed by an elementary view of those doctrines of the statical equilibrium, which are particularly applicable to constructions, and which shew the strength of timber, as it depends upon position, and in this part of the book the Author has taken occasion to introduce most of the simple mechanical powers. The principles of equilibrium are next applied to the constructions of Roofs, Domes, and Partitions, and the book ends with an excellent chapter from Tredgold, on scarfing, joints, and straps.

It was contemplated originally, to add a chapter on the nature and properties of timber, but this is rendered in a great measure unnecessary by the reprinting of Mr. Tred gold's chapter on this subject in a valuable publication, which we presume to be extensively circulated among mechanics.

Numerous practical questions are introduced to be solved by the student. Those in the second part are to be solved by the scale and compasses. More accurate solutions may indeed be obtained by calculation; but the scale and compasses, skilfully used, will give results sufficiently accurate, for practical purposes, and solutions by construction have the advantage of being conformed to the practice of carpenters, and of getting the student into the habit of drawing with accuracy.

This work is not offered to the public as a complete system of carpentry. It is designed only to furnish a familiar introduction to a most important part of it, which has been hitherto very much neglected ; and if it should be in any measure the means of convincing carpenters of the true dignity of their art, and giving them a taste for acquiring a scientific knowledge of it; the Author will think he has done no unacceptable service to the public.

With regard to the execution of the work, the Author hopes to be judged with some indulgence : for it was undertaken from a conviction that something of the kind was wanting ; and has been pursued from its commencement, without leisure, and with frequent interruptions. If however he deserves censure, he is too well persuaded of the importance of just criticism, to refuse to submit to it.