36 
SIR G. GREENHILL ON ELECTROMAGNETIC INTEGRALS. 
Fig. 3. 
A re-drawing has been made and a lantern slide, of Maxwell’s fig. XVIII, 
of the curves of constant M, or lines of magnetic force of the circular current 
round the circle AB perpendicular to the plane, on the diameter joining 
the foci, in which the confocal co-ordinates were employed of Weir’s azimuth 
diagram. 
