512 Prof. John Perry on a 



I wish to express my deep obligations to my assistant, Mr. 

 W. C. Sabine, for his valuable suggestions and for his skill in 

 the mechanical details of this investigation. 



Conclusions. 



1. The magnetic permeability of iron wires exercises an 

 important influence upon the decay of electrical oscillations 

 of high frequency. This influence is so great that the 

 oscillations may be reduced to a half oscillation on a circuit 

 of suitable self-induction and capacity for producing them. 



2. It is probable that the time of oscillation on iron wires 

 may be changed. Since I have been able to obtain only a 

 half oscillation on iron wires, I have not been able to state 

 this law definitely. 



3. Currents of high frequency, such as are produced in 

 Leyden-jar discharges, therefore magnetize the iron. 



Jefferson Physical Laboratory, 

 Cambridge, U.S. 



LXII. Table of Zonal Spherical Harmonics, calculated by 

 Messrs. C. E. Holland, P. R. Jones, and C. G. Lamb. 

 With a short .Explanation and some Illustrations of its use 

 by Professor John Perry, D.Sc, F.R.S.* 



[Plate I.] 



I HAD intended merely to present to the Society for publi- 

 cation a table of Zonal Spherical Harmonics. But some 

 Members whom I have consulted seem to think that I ought 

 also to give one or two examples of the practical use of such 

 a table. The Members of the Society will, I hope, pardon 

 my putting before them one or two elementary examples. 



The use of Spherical Harmonics in the numerical solution 

 of practical problems is almost unknown, I believe, except at 

 the Finsbury Technical College, where, every year, I have 

 been accustomed to make some Electrical Engineering students 

 work a few common examples. My students have for some 

 years been in possession of tables of zonal harmonics, but this 

 year I have thought it well to make the tables more complete 

 and to get them published for the general use of students of 

 practical physics. 



I have been told that many of the users of such a table 

 would be glad of a few statements of the general principles 

 underlying its use. For the proofs of these statements readers 



* Communicated by the Physical Society : read November 14, 1890. 



