10 Mr. 0. Heaviside on the 



out that cuprous chloride has only half the diffusibility of 

 cupric chloride. 



I am still prosecuting the investigation, and other interesting 

 relationships may be detected, but the data as to the specific 

 gravity and molecular volumes of compounds of many of the 

 rarer elements are entirely wanting, and even in the case of 

 those of well-known elements are incomplete. 



II. On the Self-induction of Wires. — Part V. 

 By Olivek Heaviside*. 



THE mathematical difficulties in the way of the discovery 

 of exact solutions of problems concerning the propaga- 

 tion of electromagnetic disturbances into wires of other than 

 circular section — or, even if of circular section, when the 

 return current is not equidistantly distributed as regards the 

 wire, or is not so distant that its influence on the distribution 

 of the wire current throughout its section may be disregarded 

 — are very considerable. As soon as we depart from the 

 simple type of magnetic field which occurs in the case of a 

 straight wire of circular section, we require at least two geo- 

 metrical variables in place of the one, distance from the axis 

 of the wire, which served before ; and we may have to supple- 

 ment the magnetic force " of the current," as usually under- 

 stood, by a polar force, or a force which is the space-variation 

 of a single-valued scalar, the magnetic potential, in order to 

 make up the real magnetic force. 



There are, however, some simplified cases which can be 

 fully solved, viz. when the external magnetic field, that in the 

 dielectric, is abolished, by enclosing the wire in a sheath of 

 infinite conductivity. It is true that we must practically 

 separate the wire from the sheath by some thickness of 

 dielectric, in order to be able to set up current in the circuit 

 by means of impressed force, so that we cannot entirely abolish 

 the external magnetic field; but we may approximate in 

 a great measure to the state of things we want for pur- 

 poses of investigation. The wire, of course, need not be a 

 wire in the ordinary sense, but a large bar or prism. The 

 electrostatic induction will be ignored, requiring the wire 

 to be not of great length; thus making the problem an electro- 

 magnetic one. 



Consider, then, a straight wire or rod or prism of any sym- 

 metrical form of section, so that when a uniformly distributed 

 current passes through it its axis is the axis of the magnetic 



* Communicated by the Author. 



