310 J. Trowbridge — Electrical Waves on Iron Wires. 



a cylinder of very porous wood ll*5 cm in diameter, 15 cm long, 

 was boiled in paratine, and a spiral was cut upon its surface. 

 The turns of the spiral were l cm apart. On this cylinder, and 

 in these spirals, the wires under examination were wound. 

 After a determination had been made with a copper wire it 

 was unwound from the cylinder and an iron or steel wire was 

 wound in the grooves occupied by the copper wire. Exact 

 geometrical similarity was thus obtained with good insulation. 

 Several hundred determinations were made with wires of dif- 

 ferent sizes. With iron wires larger than '0312 inch in diame- 

 ter no marked change in period could be noticed. If a great 

 number, however, of photographs were measured an inconstancy 

 of ratios was noticed which never appeared when the copper 

 circuits were compared. It seemed as if at certain times the 

 iron exerted a magnetic eifect and at other times failed to do 

 this. The most marked changes in period I obtained with iron 

 wires of *0312 inch in diameter. 



I give the following example. The lengths of the oscilla- 

 tions are expressed in millimetres. 



IR( 



A. 



Length of 



oscillation on 



iron circuit. 



3-7 



)N. 



B. 



Length of 



oscillation on 



time circuit. 



6-08 



COPPER. 



C. D. 



Length of Length of 



oscillation on oscillation on 



copper circuit. time circuit. 



3-5 6-14 



3-7 



6-08 



3-4 



6-00 



3-7 



5-9 



3-3 



6-00 







2-7 



5-26 



4- 



6-1 



3-4 



6-1 



~ 3-3 



5-16 



3-37 



6-56 



2-8 



3'6 



* 2-68 



3'72 



When the ratios of A to B and of C to D are compared it will 

 be seen that the time of electrical oscillations on an iron cir- 

 cuit of the same geometrical form as a copper circuit are longer 

 than those on the copper circuit. 



The rate of oscillation was not far from that I employed in 

 my investigation on the damping effect of iron wires. Since the 

 inductance appears under the square root in the formula 

 t = 27r VLc. The changes in induction due to the iron indi- 

 cated by the above table may amount to from five to ten per 

 cent. 



Thus my results confirm those of Mr. Charles E. St. John, 

 who has shown by an entirely different method that the wave 

 lengths sent out by a Hertzian vibrator on iron wires differ in 

 length from those transmitted on copper wires of the same 

 geometrical form as the iron wires. His results are even of 

 more importance in the theory of magnetism, for they deal 

 with more rapid electrical oscillations than those I employed. 



Jefferson Physical Laboratory. 



