]VIE. C. V. WALKEE ON MAGNETIC STOEMS AND EAETH-CUEEENTS. 
99 
station, or from the S. to the N. station respectively. The “ values ” are given in degrees 
of the galvanometer ah'eady described ; those under the Margate — Ashford heading are 
read off direct on the galvanometer ; those under the Margate — Eamsgate heading are 
approximate values on the same galvanometer, obtained by observation on another 
instrument, vrhich had previously been compared with the standard galvanometer. The 
majority of the observations contained in the six Tables were made at Ramsgate; in 
some cases, where an interruption occurred at that station, the blank has been supplied 
from the notes made at other stations ; in such cases the approximate value has been 
estimated and a query ( 1 ) placed beside it. The series would be complete without the 
Margate — Ramsgate values; but I have collected and tabulated these for the special 
purpose of pointmg out the very large amount of action, the great value to which a 
derived current will attain on so short a circuit as one of three miles only when well 
placed. It is very striking to read such values as 76°, 71°, 70°, 73°, 86° under such 
circumstances. They equal the effect of four or five cells in short circuit ; they exceed 
the effect from a good telegraph battery of forty-eight cells in an ordinary circuit. 
They greatly exceed what are considered good telegraph signals ; and hence we are not 
surprised to find that the ordinary battery current, as stated in the report from Dover 
already quoted, has not power enough in many instances to neutralize them. It is 
evident from these figures that wires of moderate length will suffice, especially when 
galvanometers of a more highly sensitive character than those before us are employed, 
for all the purposes of a magnetic observatory. 
I have on each day of observation calculated the mean value of the N. and the S. 
currents in time and in degrees of deflection. The most complete series of observa- 
tions are those made on September 7. They embrace a period of 9^ 28“, with blank 
periods amounting to only 40^ minutes. It is very instructive to go through such a 
Table as this, and notice the frequent transitions, not merely from N. to S. currents, 
but from a N. current of high value to a S. current also of high value, and this in the 
course of a very few minutes. For instance, between 7'’ 19-|™ and 7*^ 29'“, that is to say 
in the course of only ten minutes, four high and alternate values are registered, 64°, 44°, 
34°, and 38°. Many other like cases may be selected from the Tables before us. 
These six groups of selected observations are analysed in Table IX. The total 
number of currents recorded on the six days are arranged according to their values in 
time. The number of currents on each day that had a duration of and f min. are 
first given ; then those of various lengths between one and five minutes ; and finally 
those for each interval of five minutes, beginning with those from six to ten minutes, 
and terminating with those between 61 and 120 minutes, which is the limit. The 
results of each day are given under the respective columns in the division of the Table 
marked a; and the sum for each time- value is given in the last column. Only 19 out 
of 389 currents, or 1 in 20, had a duration of less than a minute. The proportion between 
those currents which exceeded, and those which did not exceed five minutes in duration, 
was as 117:272, or as 1 : 2‘32. Of those which exceeded twenty minutes and those 
which fell between six minutes and twenty minutes, the proportion was 26: 91, or 
p 2 
