40 Scientific Proceedings, Royal Dublin Society. 



direction as the electro-magnetism of the cores, and not reversing the current 

 at any time during the taking of a set of records. 



Thus we obtained curves which, though possessing but a bi-lateral 

 symmetry about the interpolar axis, are not otherwise distorted. 



The curvature of the diameter and non-coincidence of the E. P. and 

 C.F. are due to the combined effects of the magnetism of the sole, and the 

 earth's horizontal field — but it is beyond the scope of this paper to analyse 

 these effects singly. 



The latter might be eliminated entirely by working in a closed chamber 

 with thick walls of soft iron. Effects due to permanent magnetism of the 

 iron might be eliminated by making the electro-magnet of laminated Swedish 

 charcoal iron throughout. 



In presenting our results we lay stress on the following points : — 



(i) The path of the body depends upon its size. 



(ii) The field in which it moves is not constant. It is, in fact, the resultant 

 of the earth's field and a parallel field, whcih is varied in intensity for reasons 

 already shown. 



(iii) The presence of the body modifies the geometrical configuration of 

 the field. 



We realize that there are serious objections to be overcome in order to 

 obtain quantitative results, and that the curves we show are the paths of one 

 particular body moving in one particular resultant field; but we consider 

 that such results are a first approximation to the experimental solution of a 

 difficult problem. 



This investigation was made to supply the approximate physical data 

 demanded for biological phenomena by one of the authors ; and has supplied 

 to him what was needed. As his collaboration now ends, we must apologize 

 for presenting a research in a state which may be critized as inchoate by the 

 professed physicist. 



Note. — During the interval that elapsed between the reading of this 

 paper and its publication, Dr. Felix E. Hackett (Eoyal College of Science, 

 Dublin) has pointed out from theory that in the horizontal plane through 

 the poles NN' there is a maximum for the magnetic force along the 

 perpendicular bisecting NN' at 0, at a point P, such that OP = ON x -708. 

 and hence P is a rest point. This is not in accordance with the results of 

 our experiments, and I hope shortly to investigate the discrepancy. Professor 

 Bergin, m.a. (University College, Cork), also mentioned this, and showed 

 that there are other maxima along lines prallel to OP. These would not be 

 found by our method of experiment ; but might be shown if the particle were 

 constrained to move (say) in perfectly smooth glass tubes. These maxima soon 

 disappear as either pole is approached. — P. E. B. 



