106 Mr. J. E. Moore on a Continuous and 



inconsistent with the existence of a current of about a tenth 

 or a twentieth of that amount ; but on account both of the 

 smallness of the results and of the discrepancy between the 

 values obtained for 1891 by two methods, we cannot assert 

 that such a current actually exists. The calculations taken 

 by themselves do not disprove the hypothesis that electric 

 currents traverse the earth's surface, as we cannot argue from 

 the condition of a small portion of the globe to that of the 

 whole. The most that can be said is that no evidence in 

 favour of the existence of vertical currents can be drawn from 

 one district, which has been very minutely surveyed. 



P.S. — No reference to Dr. Schmidts original paper was 

 given in the short notice published in the Report of the 

 British Association. I had therefore supposed that the latter 

 was a preliminary note. Professor Schuster has, however, 

 recently shown to me Dr. Schmidt's complete investigation, 

 and he has kindly calculated the current-density at latitudes 

 50° and 55° on the prime meridian from formulae given by 

 Dr. Schmidt. The result is upward currents and 0'20 to 0'15 

 ampere per square kilometre at lat. 50° and 55° respec- 

 tively. The mean of these two numbers, viz. 0*175, is nearly 

 equal to Schmidt's mean for the whole earth (0*17). It is 

 opposite in direction to and very much greater in magnitude 

 than any vertical current the existence of which is compatible 

 with the results of the Magnetic Survey. 



XIII. A Continuous and Alternating Current Magnetic Curve 

 Tracer. By John Ely Moore, M.E., E.E.* 



§ 1. (\^ the various methods that have been proposed and 

 Vy used for measuring the magnetic quality of iron, 

 or the losses of energy in iron due to magnetic reversals, 

 none have been successful as accurate means of measurement 

 that have not given simultaneous and independent readings 

 (capable of interpretation in absolute units) of the two quan- 

 tities, magnetic induction or intensity of magnetization, and 

 the magnetizing force producing that induction. 



In a magnetic-curve tracer intended for accurate work, the 

 first condition to be fulfilled is that its indicating system 

 shall be capable of receiving and recording two simultaneous 

 and independent displacements, always at right angles to each 

 other, and always strictly proportional, respectively, to the 

 intensity of magnetization of the sample under test, and the 

 magnetizing force producing that magnetization. 



* Communicated bv the Author. 



