453 



MISCELLANEOUS INTELLIGENCE, 



^ I. Mechanical Science. 



1. On the Adhesion of Screws. — ^The following results, respecting 

 the force necessary to draw iron screws out of given depths of wood, 

 are by Mr. Bevan, and should be placed by the side of those he has 

 given with regard to nails*. 



" The screws I used were about two inches in length, 0.22 dia- 

 meter at the exterior of the threads, 0.15 diameter at the bottom, 

 the depth of the worm or thread being 0.035, 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 r 



Dry beech 460 pounds 



Do. Do 790 



Dry sound ash 790 



Dry oak 760 



Dry mahogany 770 



Dry elm 655 



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 woods about half the above. 



*' From which we may infer as a rule to estimate the full force of 



adhesion, in hard wood 200.000 d ^ t =: f 



and in soft wood 100.000 d ^ t := f 



d being the diameter of the screw ; o the depth of the worm or 

 thread ; and t the thickness of the wood into which it is forced ; — 

 all in inches; /"being the force in pounds io extract the same." 

 We may, from the above experiments, observe the approximation to 

 perfection in the art of screw making ; for had the screw been 

 greater in diameter, there would have been a waste of material, or 

 had it been less, it would not have been sufficiently strong, which 

 may be proved as follows : the cohesion of wrought iron has been 

 found, from a number of experiments, to be about 430001bs. per 

 cylindrical inch ; and as the smallest diameter of screw used in my 

 experiment was 0.15, it would have been torn asunder by a force 

 of about 9681bs. ; or if the hard wood had been about -^ of an inch 

 thick into which it had been screwed, the screw would have been 

 broken instead of forcing its passage out of the wood. — Phil. Mag. 

 N.S.iu29i. 



2. Improvement in Steam-engines. — According to the valuable 

 records kept of the duty of the steam-engines at the mines in Corn- 

 wall, a most important improvement has been effected in two 



♦ See page 860, vol. xvii. of the former series of this Journal. 



