80 Prof. A. E. H. Love. The Advancing Front of the [May 9, 



described round the centre of one of Hertz's figures, and the parts of 

 his lines of force which lie outside that circle should be suppressed 

 and their places taken by curves of the family traced in fig. A. The 

 result that at the beginning of the vibration the moment of the 

 doublet is a maximum would be expressed by taking his figures in the 

 order 29, 30, 27, 28. After the electromagnetic field has become 

 established, these figures represent the field near the vibrator at 

 instants which are the beginning of a period, of a period later, J of 

 a period later, % of a period later. If the arrow heads in his figures 

 are reversed, they represent in the same order the field after J a 

 period, f of a period, f of a period, I of a period from the beginning 

 of a particular vibration, which is not the first vibration. To trace 

 the course of the first vibration we should proceed as follows : At 

 the instant when the vibrations begin the field is that shown in fig. A. 

 After J of a period draw on Hertz's figure 30 a circle of radius J A,* 

 suppress the part of the figure outside this circle and replace it by the 

 part of fig. A which is outside the same circle. To obtain the fields 

 after period and |- period, similar work should be done upon Hertz's 

 figures 27 and 28 with circles of radii A, f A. After | a period, 

 reverse the arrow heads in Hertz's figure 29, draw on this figure a 

 circle of radius JA, suppress the part of the figure which is outside 

 this circle and replace it by the part of fig. A which is outside the 

 same circle. To obtain the fields after | period, f period, | period, 

 similar work should be done upon the figures 30, 27, 28 with circles 

 of radii A, f A, JA. These modified figures have not been drawn here 

 because a similar procedure will be adapted presently to the figures 

 of Pearson and Lee in which account is taken of the damping by 

 radiation. 



The notation of this paper can be identified with that of Pearson and 

 Lee by means of the equations 



t' = t + /C, El = -A0"l\ 2r = A/c, X = T-^ ... (18), 



2i A 



in which the quantities El, T, x are used by these authors,! and f is 

 the quantity which they denote by t. They have traced the lines of 

 electric force, given by Q = constant, for certain chosen values of Q for 

 a region of space between the spheres r = ^ A and r = f A, and for 



.fty-six values of f, viz. : f = 2r (J, J, ...7). The chosen values of Q 

 are such that QA/2,E/= T ^, A , ^ J> The curyeg ^ 



ormed are shown m their Plates 1-7, each plate containing eight 

 figures.J The chosen value of v is 0-4. 



has U9ed the 

 t 2r is the period. 



