20 



IV.-Mechax.cal properties. ;. ..■ properties based on elastic, coudilions exhibited by the aggregate masB under 

 inllucuce of exterior (moehiiuical) forces. 

 (a) rorm changes wilhontdeslnicUon of cohcxion, coi.m.only called chisticity, llexil.iUty, toughuess. 

 \l>) Farm changes "nth des,n,cUon of cohesion, co.um.mly .■ailed strcugth (tensile, compressive, torsioual, shearing), 



eleavability, hardness, 

 v.— Technical PROPERTIES, j. c., properties in conibination. 



Here would be considered the woods with reference to their technical use. tl,c.r applicatn.n n, I l,e a.ts, 

 which is invariably based npou a, c.nnbination of several physical or mechanical properties. 



VI.— Diseases ^vxD FAULTS. , j. ■ i „ i;,i ,,.. 



Herewonld be treated the changes in structure ami properties irom the normal to ab.mnna] co,„l,l,u„s, 



duo to influences acting upon the tree during its life or upon the tiiuber durmg its use. 

 V/ 1.— Relation of properties to each other. , • i , ■ , 



Here would be discussed the e.m.iection which may be established between st rueture, physical, ehemieal 

 and mechanical properties, and also between these ami the conditions of growth und..r which the material 

 was produced. The philosophy of the entire preceding knovvledge would here be brought together. 



To contribute toward this impoit:uit braiu'h of Immau knowledge, and to help in the bnilding 

 of its foundation, the work, undertaken by th.> Division of Forestry, described in this bulletin, 

 was designed by the writer; and, in order to build with a knowledge of what has been done before 

 on this structure, a brief review of the progress in the development of timber physics seemed 

 advisable. In this I have followetl largely the excellent resume by Dr. W. F. Exuer m Lorey's 

 Handbuch der Forstwissenschaft. 



HISTORICAL. 



The first important and exhan-stivc work was that of Parent, publisli.d in tlie Menioires de 

 I'Academie des Sciences in the years 1707 and 1708, being "investigations into the strength of oak 

 and lir." The idea of elasticity, so important in the application of timbers, was not even known to 

 him. A work memorable in tliis tirst period of scientilic cttorts in this direction was produced by 

 MUSCHENBROBCK in 1762 (Introductio ad p'.iil(Uo;)hia:n iiaturalcm), discussing especially the 

 differences of strength in the different parts of the same tree. Although not a sufficient number of 

 satisfactory experiments were conducted to prove his deductions fully, they were remarkably clear 

 and in the main correct. The celebrated naturalist, BuffoN (Oeuvres, Vol. x), occupied himself in 

 a comprehensive manner with a determination of the mechanical properties of oak wood. In 1780 

 apiic.ired the often-cited work of Duhamel DuMoncbau, Traite de la Conservation ct de la 

 Force, which contains a number of references to tlie properties of timber. 



These three authors are abnost the only ones who occupied tliemselves with the determination 

 of density and strength in the different parts of the same tree and of tlie inrtuence of soil conditions 

 on these properties. The contradictions in their views and deductions, however, left these 

 important questions undecided. < )nly the authors of later periods gave any tliought to tlie study 

 of elaisticity. Among these were Oibard (Traite Aiialytique de la R'^sistance des Solides, 1798), 

 who experimented on oak columns, and Perronnet (Memoires sur les pieux et les pilotis, 1782). 

 The latter found that a contiiuums even load increases the depth of detlection, which he argues 

 could not be the case without a change in elasticity, by losing part of its energy. At the end oi' 

 the last and the beginning of this century a immber of recognized men of science lia\e determined 

 by experiment, for a large number of timbers of tlifterent kinds and locality, the density, tlie 

 strength, and the coefacient of elasticity. :N"otable among these are Bblidor (Architecture 

 hydrauUque, 1782), Rondelet (Art de batir), Barlow (Essay on the strength of timber, 1817), 

 Ebb ELS, and Tredgold in various works. 



Charles Dnnx published in the Journal de ri5c:)le Polytechni(iue, Vol. 10, 1815, an exten- 

 sive work on the mgiihanical properties of wood (Experiences sur la tlexibilite, la force, et rclasticit6 

 des bois). He investigated the nature of the elastic curve, the position of the neutral plane (fibre 

 inrnriable), and he corrected the formulas which express the relations of the size of test pieces and 

 the applied loads to the resulting d eflections. 



Bevan occupied himself especially with the determination of the modulus of elasticity, derived 

 from experiments in torsion. (Philosophical Transactions, 1829.) 



8AVART utilized tone vibrations of wooden plates in order to determine the differences of 

 elasticity and the position of its axes. Tliese plates were cut from a piece of beech, in various 



