228 ANSWERS TO QUERIES. 



by the writer some time since ; firstly — a piece of iron, about 

 three inches long, and a quarter of an inch thick, with a notched 

 head at one end, like a three inch screw, was placed horizontally 

 in a hole, in which it could be made to turn with any degree of 

 friction ; a nine inch screw-driver was then placed, with the 

 end of the blade in the notch of the screw, while the handle was 

 retained in the line of direction of the screw, by means of a stee! 

 point acting on the opposite, and through an upright puppet head : 

 a lever of a given length was screwed into the handle, at right 

 angles to the blade, or what amounted to the same thing, a wheel 

 of a given diameter was fastened upon the handle, so as to revolve 

 with the screw-driver. On a groove in the circumference of the 

 wheel passed a cord, having a hook at the end, by attaching 

 weights to which the power neceasavy to cause the screw-driver 

 and screw to revolve could be easily estimated. 



Secondly — this power being ascertained, the short screw-driver 

 was removed, and a screw-driver, 2 feet 4 inches in length, mounted 

 in a similar manner, "was substituted, and the weight necessary 

 to turn it was found to be precisely the same. 



Thirdly — greater friction was given to the screw, and the 

 former experiments were repeated with the same result. The power 

 required to turn each screw-driver being the same. 



Fourthly — the experiment was varied by substituting for the 

 screw-drivers, a flat blade of steel, four feet long, having a handle 

 and wheel which slid upon it and which could be fixed at any 

 distance from the head of the screw, and it was found, that the 

 power required to overcome any given degree of friction W3S the 

 same at all distances; hence it is evident that no absolute me- 

 chanical power is gained by a long screw-driver over a short one. 

 The advantage is simply this, with a short screw-driver the bands 

 of the operator are employed almost close together; consequently 

 very little steadiness can be ensured, and a very slight deviation 

 from the perpendicular causes one comer of the flat end of the 

 blade to lift out of the notch, and thereby slip and mutilate the 

 screw ; whereas, a long screvy-dviver is not only more easily kept 

 in its position, but affords, by its great distance from the work, 

 more room and consequently greater facility for the application 

 "of muscular exertion, which is actually the only advantage 

 gained . 



«IV\ — Why does a wedge shaped piece of timber require 

 less force to draw it through water, with the butt end than with 

 the sharp end foremost ? " 



