[From the Report of tJie British Association, 1856.] 



XI. On a Method of Drawing the Theoretical Forms of Faraday's Lines of 



Force without Calculation. 



/ 



THE method applies more particularly to those cases in which the lines 

 are entirely parallel to one plane, such as the lines of electric currents in a 

 thin plate, or those round a system of parallel electric currents. In such cases, 

 if we know the forms of the lines of force in any two cases, we may combine 

 them by simple addition of the functions on which the equations of the lines 

 depend. Thus the system of lines in a uniform magnetic field is a series of 

 parallel straight lines at equal intervals, and that for an infinite straight electric 

 current perpendicular to the paper is a series of concentric circles whose radii 

 are in geometric progression. Having drawn these two sets of lines on two 

 separate sheets of paper, and laid a third piece above, draw a third set of lines 

 through the intersections of the first and second sets. This will be the system 

 of lines in a uniform field disturbed by an electric current. The most interesting 

 cases are those of uniform fields disturbed by a small magnet. If we draw a 

 circle of any diameter with the magnet for centre, and join those points in which 

 the circle cuts the lines of force, the straight lines so drawn will be parallel and 

 equidistant ; and it is easily shown that they represent the actual lines of 

 force in a paramagnetic, diamagnetic, or crystallized body, according to the 

 nature of the original lines, the size of the circle, &c. No one can study 

 Faraday's researches without wishing to see the forms of the lines of force. 

 This method, therefore, by which they may be easily drawn, is recommended 

 to the notice of electrical students. 



VOL. I. 31 



