TO PROFESSOR FARADAY.

       Marischal College, Aberdeen,
      30th November 1859.

     DEAR SIR—I am a candidate for the Chair of Natural  Philosophy in the University of Edinburgh, which     will soon be vacant by the appointment of Professor J. D. Forbes to St. Andrews. If you should be able, from   your knowledge of the attention which I have paid to science, to recommend me to the notice of the Curators, it   would be greatly in my favour, and I should be much indebted to you for such a certificate.

     I was sorry that I had so little time in September that I could not write out an explanation of the figures of lines of    force which I sent you; but Professor W. Thomson, to whom I lent then, seems to have indicated all that was   necessary, and most of them can be recognized from their resemblance to the curves made with Iron filings.

     The only thing to be observed is, that these curves are due to the action either of long wires perpendicular to the  paper, or of elongated magnetic poles, such as the edge of a long ribbon of steel magnetised transversely. By   considering infinitely long currents or magnetic poles perpendicular to the paper we obtain systems of curves far   more easily traced than in any other case, while their general appearance is similar to those produced in the   ordinary experiments.

     All the diagrams have two sets of lines at right angles to each other, and the width between the two sets of lines is    the same, so that the reticulation is nearly square. If one system belongs to poles, the other belongs to currents, so  that if the meaning of one be known, that of the other may be deduced from it.—I remain yours truly,

                                                 JAMES CLERK MAXWELL.