CATALOGUE.— PHLOSOPHY AND ARTS, PRACTICAL MECHANICS. I5y 



Girard Traite de la resistance dcs solides. 

 Paris, 1797. 



The historical part of the preface is the only thing of va- 

 lue that the work contains. 



On the strengtli of beams. Banks on ma- 

 chines. 73. 



On steel. Nich. I. 468. 11. 64. Stodart, Nich. 

 IV. 127. 



A wire of -L inch of lead breaks witli 29i pounds ; of tin 

 with 491 ; of copper with aggi; of brass with 360; of 

 silver with 370; of iron with 450; of gold with -500. 

 Emerson. 



A yard of oak an inch square will bear in the middle for 

 a very short time 330 pounds. But, according to Emerson, a 

 third or a fourth of this is as much as can be applied in 

 practice. Mech. p. 114. It is in fact much more; for in 

 general the weight supported ought not to produce a sensi- 

 ble bending ; and this practical limit requires more atten- 

 tion than it has hitherto received. Allowance must also be 

 made for the occasional depredations of insects. 



Wood is from 7 to 20 times weaker transversely than 

 longitudinally. It becomes stronger both ways when dry. 



Proportional strength of various substances in bearing 

 pressure. Fine freestone 1 : alder, asp, birch, white fir, 

 willow, 8: lead, 61: beech, cherry, hasel, 6|: red fir, 

 holly, elder, plane, apple, 7 : walnut, thorn, T\ : elm, ash, 

 8^ ; box, yew, plumbtree, oak, 1 1 : bone, 22 : brass, 50 : 

 iron, 107. These results however differ materially from 

 some others. 



A cylinder an inch in diameter will bear, when loaded to l 

 of its whole strength, if of fir 8.8 cwt., if of rope 22 cwt., if 

 of iron O.75 tons, or 135 cwt. Emerson. 



Count Rumford found the cohesive strength of a cylinder 

 of iron an inch in diameter 63466 or 63173 pounds ; the 

 mean 63320. Ph. tr. 1797. This is only Jj more than 

 Emerson. 



Sickingen makes the comparative cohesive strength of 

 gold 150955, of silver 190771, of platina 262361, of copper 

 304696, of soft iron 362927, of hard iron 5598SO. Gilb. 

 Journ. Guyton makes platina a little stronger. 



In Buffon's experiments, h, d, and / being the breadth, 

 depth, and length of a beam of oak in inches, the weight 



(54 25 <. 

 '■ 10). Robison. 



A piece of sound oak an inch square bears gooo pounds di- 

 rectly, and is broken transversely by 200 at the distance of 

 12 inches from the fulcrum. Iron is not cheaper than 

 wood of equal strength. The immediate transverse strength 

 of lateral adhesion of most substances eiceeds their direct 



VOL. II. 



cohesive strength, but the difference is less in fibrous sub- 

 stances than in others. Robison. Coulomb found them 

 nearly equal. 



Six of the pieces of oak employed in Girard's experiments 

 broke under the pressure of 2710 pounds on a square incli 

 at a mean ; but 1 5 others supported a much greater load. 



Aribofcasrironwithabutmentsof29§feetspan, 1 1 inches 

 high in the centre.supported 11130 pounds, but sunk 3Z 

 inches, and rose again | inch: without abutments it broke 

 with 6174 pounds. Bars of iron i inch square and 3 fett 

 long, weighing y pounds, sunk about an inch, and broke 

 with 960 pounds. In general iron is about 4 times as strong 

 as oak, and 6 times as strong as deal. Banks on machines, 

 93. 



The hardness of metals follows this order, iron, platina, 

 copper, silver, gold, tin, lead. C^vallo. II. 147. 



When a body is broken by means of an impulse of any 

 kind, there is a certain velocity which is sufficient to pro- 

 duce firacture, whatever may be the bulk of the impelling 

 body. Thus, supposing any body to be capable of being 

 compressed or extended one hundredth part of its length, 

 this effect will require the pressure of the hundredth part 

 of the weight of the modulus of elasticity, or the impulse of 

 the same weight falling through J^ of the length, or the 

 impulse of a weight equal to its own, falling through -^ of 

 the height of the modulus, and acquiring a velocity equal 

 to one hundredth of that which is due to half the height 

 of the modulus : this is therefore the utmost velocity 

 that the particles of such a body can receive without 

 exceeding the limit at which a separation takes place ; and 

 it is for this reason that a body, moving very rapidly, carries 

 before it only the part of the substance which is in immedi- 

 ate contact with it, and does not extend its effects any fur- 

 ther. The same limit may also be derived from a consider- 

 ation of the velocity with which an impulse is transmitted 

 through any substance. 



A body being broken by a force directed to a point at the 

 distance a from the axis of a beam, of which the depth is b, 

 the strength is to the direct cohesive or repulsive strength 

 as b to 6a±i, accordingly as the beam gives way 6n the 

 side next to the force or on the opposite side. 



Friction, 

 Amontons on the resistance of machines. A. 



P. 1699.206. H. 104. 1700. 47. 1703. H. 



105. 1704. 173. 206. 



Allows about | of the weight. 

 Pixrenton the centre of friction. A. P. 170O. 



H. 149. 



