112 Mr. Tredgolcl on the Ttieory of Hydro-dynamics. 



Upon examining the separated surfaces, the glue appeared to 

 be very thin, and did not entirely cover the wood, so that the 

 actual cohesion of glue must be something greater than 715 

 pounds to the square inch. 



I also tried the lateral cohesion of fir-wood, from a Scotch 

 fir of my own planting, cut down in the autumn of 1825, and 

 sawn into boards, being at the time of this experiment quite 

 dry and seasoned. The force required to separate the wood 

 was 562 pounds to the square inch ; so that if two pieces of 

 this wood had been well glued together, the wood would have 

 yielded in its substance before the glue. 



The cohesion of Memel fir, across the grain, I have found 

 to be from 540 to 84-0 pounds to the square inch, on a speci- 

 men tried some time ago, the modulus of elasticity of which 

 in the same position of the grain, varied from 40,500 to 44,600 

 pounds ; and the modulus of elasticity of the Scotch fir tim- 

 ber used in the experiment above described, was 24,600 

 pounds. 



I also tried the force required to break, or tear out, a half- 

 inch iron pin, applied in the manner of a pin to a tenon in 

 the mortice; the thickness of the board being 0*87 in. and 

 distance of the centre of the hole from the end of the board 

 1*05 in.; — the force required was 976 pounds. As the 

 strength of a tenon, from the pin-hole, may be considered in 

 proportion to the distance from the end, and also as the thick- 

 ness ; we may, for this species of wood, obtain the breaking 

 force in pounds nearly, by multiplying together one thousand 

 times the distance of the hole from the end, by the thickness 

 of the tenon in inches. I am, dear sir, yours truly, 



B. Bevan. 



P.S. From an experiment subsequently made on solid glue, 

 I find the cohesion to be 4000 pounds to the square inch, from 

 which it may by inferred that the application of this substance 

 as a cement is susceptible of improvement. B. B. 



XV. Researches 07i the Theory of Hydro-dynamics. /&/ Thomas 



Tredgold, Esq. Civil Engineer. 



[Second Communication.] 



Prop. 1. — r PHE resistance to the motion of a body in a fluid 



■*• is equal to the quantity of motion it impresses 



on the fluid. 



For, if the quantity of motion were greater than the resistance, 

 the effect would be greater than the power producing it, and if it 

 were less, the resistance would be greater than the resisting 

 forces. 



Prop. 



