^■64. PROFESSOR MOSELEY, ON THE THEORY OF 



two parts into which this surface divides the system ; then the locus of the 

 consecutive intersections of these resultants is that curved line to which I 

 have assigned the properties of equilibrium described in the preceding page. 



I wish now to correct this definition. 



To the properties assigned to this line it is necessary that at each of 

 the points where it intersects contiguous surfaces of the component masses, 

 the whole pressure upon those surfaces should be supposed to be applied. 

 Now, according to the definition given of it, this supposition is not, except 

 under certain circumstances, admissible. 



The resultant of the pressures upon each surface of contact is necessarily 

 at some point or other a tangent to the locus of the intersections of the 

 resultants, but it mmj be, and except in particular cases, will be, a tangent 

 to it at a point other than that in which this line intersects the surface 

 of contact itself. 



The point where the resultant intersects the dividing surjhce to which 

 it corresponds, is that element in the theory on which the condition, " that 

 one portion of the system shall not turn over upon the boundary of its 

 surface of contact with the adjacent portion," depends. I propose, there- 

 fore, in the following paper, to determine the line which is the locus of 

 intersections of the consecutive resultants, with the corresponding imaginary 

 surfaces of division, these surfaces being, here, supposed to be planes. 

 This line I shall call the Line of Resistance, including as it does 

 the points of application of the resultants of all the resistances of the 

 surfaces of contact. 



The direction in which the resultant intersects two common surfaces 

 of contact, is that on which the condition, "that these surfaces shall not 

 slip upon one another," depends ; moreover this direction is a tangent to 

 the line which is the locus of the intersections of the consecutive resultants, 

 drawn from the point where the line of resistance cuts the surface of 

 contact. The determination of this line is therefore also an important 

 feature in the theory. I propose that it should retain the name before 

 given to it of the Line of Pressure. 



