TRANSACTIONS OF SECTION A. 567 



3. On the Measurement of the Length of Electro-magnetic Waves. 

 By Professor Oliver J. Lodge, F.B.S. 



The author has been endeavourinij: to manufacture light by direct electric action 

 ■without the intervention of heat, utilising for the purpose Maxwell's theory that 

 light is really an electric disturbance or vibration. 



The means adopted is the oscillatory discharge of a Leyden jar whose rate of 

 vibration has been made as high as 100 million complete vibrations per second. 



The waves so obtained are about three yards long, and are essentially light in 

 every particular except that they are unable to afiect the retina. To do this they 

 must be shortened to the hundred-thousandth of an inch. All that has yet been 

 accomplished, therefore, is the artificial production of direct electrical radiation 

 differing in no respect from the waves of light except in the one matter of length. 



The electrical waves travel thi-ough space with the same speed as light, and are 

 refracted and absorbed by material substances according to the same laws. It 

 only wants to be able to generate waves of any desired length in order to entirely 

 revolutionise oiu" present best systems of obtaining artificial light by help of steam 

 engines and dynamos, which is a most wasteful and empirical process. 



The author measures the waves by converting them into stationary ones by 

 the interference of direct and refiected pulses at the free ends of a long pair of 

 wires attached as appendages to a discharging Leyden-jar circuit. The circuit 

 and its appendages are adjusted till a recoil kick observed at the far end of the 

 wires is a maximum, and the length of each resonant wire is then taken to be half 

 a wave-lengtli. The length so measured agrees with theory. 



4. On the Impedance of Conductors to Leyden-jar Discharges. 

 By Professor Oliver J. Lodge, F.B.S. 



In the course of a series of experiments on the theory of lightning-conductors 

 the author had devised an arrangement for testing the electromotive force necessary 

 for sending a given discharge through a given conductor, and thus for comparing 

 the obstruction or impedance which various conductors ofiered to such discharges. 



The results were compared with the general theory of Clerk Maxwell and Lord 

 Rayleigh, and were such as entirely to confirm that theory, although at first sight 

 they were paradoxical and surprising. 



The apparent resistance was some hundred thousand times greater than would 

 have been obtained for steady currents ; and for verv high frequencies of alternates, 

 say over a milhon per second, it was almost independent of the diameter and quite 

 independent of the material of the rod used. In fact, the ordinary laws of conduc- 

 tion fail utterly and a new condition of things obtains. 



Iron carries off Leyden-jar discharges quite as well as copper, and apparently 

 in some cases even better. All but this last anomaly are susceptible of complete 

 explanation in the light of the theory of JMaxAvell and Lord Eayleigh and Mr. 

 Oliver Heaviside, and the experiments verify that theory. 



5. A simple hypothesis for Electro-magnetic Induction of incomplete circuits, 

 with consequent equations of Electric Motion in fixed homogeneous or hetero- 

 geneous solid matter. By Professor Sir William Thomson, LL.D., F.B.S. 



1. To avoid mathematical formulas till needed for calculation consider three 

 cases of liquid' motion, which for brevity I call Primary, Secondary, Tertiary, defined 

 as follows ; Half the velocity in the Secondary agrees numerically and directionally 

 with the magnitude and axis of the molecular spin at the corresponding point 

 of the Primary ; or (short, but complete statement) the velocity in the Secondary is 

 twice the spin in the Primary ; and (similarly) half the velocity in the Tertiary is 

 the spin in the Secondary. 



' I use ' liquid ' for brevity to signify incompressible fluid. 



