LONG-WAVE RADIO TELEPHONE TRANSMISSION 695 



APPENDIX I 

 Measures of Terrestrial Magnetic Activity 



"C" AND "m," 



Characferization (C) 



"Terrestrial-magnetic activity at a given station, and in a certain 

 interval, may be defined as an expression for the frequency and 

 intensity of magnetic disturbances in that interval. There are many 

 ways in which this general definition may be expressed as a numerical 

 measure. Characterization, the simplest, is now widely used. In this 

 measure every observatory assigns, from the character of its photo- 

 graphic records, to each interval of 24 hours, between successive 

 Greenwich midnights, a character-figure, '0' for quiet, '1' for moder- 

 ately disturbed, and '2' for greatly disturbed days. The average for 

 all collaborating observatories (the number of which increased from 30 

 to about 45, since this measure was begun in 1906) is the international 

 magnetic character-figure C." ^° 



"A primary desideratum is to arrive at a clear idea of exactly what it 

 is we want to measure. If our object is simply to discriminate between 

 the days of a single month, with a view to selecting for special purposes 

 the five quietest or five most disturbed days of the month, it is very 

 doubtful whether the existing scheme of international 'character' 

 figures can be improved on. Its simplicity and the small amount of 

 labor it entails are great recommendations. The disadvantages it 

 seems to me to possess are: 1. The significance of any particular 

 'character' figure, e.g., 1.5, is variable; it connotes decidedly less 

 disturbance in a quiet than in a disturbed year. Also, while the mean 

 'character' figure for the year does to a certain extent wax and wane 

 with disturbance, the variation seems to me inadequate. 2. The 

 assigning of 'character figures' at an individual station is largely a 

 psychological process, depending on the temperament and knowledge 

 of the judge. The standards in use at different stations at the same 

 time are widely different, and the standard in use at any particular 

 station may vary largely from time to time. The 'character' figures 

 supplied by any two stations do not suffice for a satisfactory inter- 

 comparison of the stations, and if we wish to compare one year or 

 season with another the international 'character' figures leave a great 

 deal to be desired." " 



The "C" measure of magnetic activity may be inferior as a basis 

 for comparing years, but is relatively safe for comparing short intervals 

 such as days within a month. For comparing longer intervals a 



