Mr. Bevan on the Adhesion of Screws. 291 



pelled to slip their cables, until in like manner the evil has in- 

 creased to an alarming extent, — a calamity that might hence- 

 forth be avoided, at an expense scarcely eqtml to the value of 

 one riclili) freighted vessel. How many valuable India-men 

 have been lost in sight of home, after escaping the perils of a 

 long voyage, merely for the vi'ant of a security that can be af- 

 forded them at a comparatively trifling expense ! 



Yours, &c. 

 George-street, Hanover-square. J, P. De la Fons. 



XLVIII. On the Adhesion of Screws. By B. Bevan, Esq., 

 Civil Engi7ieer.* 



"VTEXT to that of nails, there are few things in more general 

 ■^ use amongst artificers than screws. I do not recollect 

 seeing in any publication the results of any experiments on 

 the force necessary to draw screws of iron, commonly called 

 wood screws, out of given depths of wood. Having here- 

 tofore published the force necessary to extract nails driven 

 into wood, the following results of my experiments on the force 

 required to extract screws, made some time ago, may be of 

 some interest. 



The screws I used were about two inches in length, -^^^ 

 diameter at the exterior of the threads, yg^^ diameter at the 

 bottom, the depth of the worm or thread being j^^q, and the 

 number of threads in one inch =12. They were passed 

 through pieces of wood, exactly half an inch in thickness, and 

 drawn out by the weights specified in the following table : 



Dry beach 4-60 lbs. 



Ditto ditto 790 



Dry sound ash 790 



Dry oak 760 



Dry mahogany 770 



Dry elm Q55 



Dry sycamore 830 



The weights were supported about two minutes before the 

 screws were extracted. 



I have also found the force required to draw similar screws 

 out of deal and the softer wood about half the above. 



From which we may infer, as a rule to estimate the full 

 force of adhesion, in hard wood... 200,000 dlt =.f 

 and in soft wood... 100,000 dlt =f 

 d being the diameter of the screw; 8 the depth of the worm 



* Communicated by the Auilior. 



2 I' 2 or 



