284 Mr HARRIS'S Experimental Inquiries concerning 



for this purpose, so that the adjusting apparatus rests on a base 

 independent of that which sustains the rest of the machine ; and 

 when it is required to examine the same force, the bar being 

 placed in an horizontal position, it is then laid on the horizontal 

 plane before mentioned (10.), and represented in Fig. 9, the 

 divided scale my being now a detached piece of wood or brass, 

 fixed against one of the perpendicular sides of a right-angled 

 triangle, it can thus be transferred to any part of the bar. There 

 is a small spirit-level occasionally placed on the plane AB, in or- 

 der to indicate, as nearly as possible, the horizontal position, when 

 adjusting the distance by means of the screws S, S, Fig. 9. 



13. The iron or magnet a?, Fig. 1, and the cylindrical counter- 

 poise W, being accurately suspended, and the index adjusted at 

 zero, if the least impulse be communicated to either side, a long 

 continued and delicate oscillation will take place before the in- 

 dex again returns to its point of rest, which it finally does at 

 zero, thus evincing great freedom of motion. 



The accuracy of the whole machine should now be finally 

 examined, by placing successively small weights of a grain or 

 more, according to the dimensions of the cylindrical counter- 

 poise, first on the suspended body ae, and afterwards in the he- 

 mispherical cup at o. Thus, if one grain moves the index in ei- 

 ther direction 5 degrees, two grains should move it 10 degrees, 

 and so on ; and the motion on each side of zero should corre- 

 spond. 



Beside the certainty we thus obtain of the accuracy of the in- 

 strument, or the error to which it is liable, we are enabled to 

 refer the force indicated to a known standard of weight, which 

 is every where the same, it being only necessary to state the dis- 

 tance at which the force acts, and the dimensions of the body x, 

 supposing it to be of soft iron of the ordinary kind. Thus, if 

 the distance should be an inch, and the index marking 25, we 



