MAGNETIC DISTURBANCES AT SEVERAL OBSERVATORIES. 
133 
surface do not differ very greatly from one another. A direct comparison of the 
several photographic records reduced to Greenwich mean time shows in a very marked 
manner that the character of a disturbance is the same over a very wide area of the 
Earth’s surface, and that the different phases of the disturbances take place at the 
different stations at the same instant of time. 
In .the present paper a comparison is made of more recent magnetic disturbances in 
June, 1885, at ten other observatories in addition to the seven observatories whose 
records were previously compared. 
Quite recently two additional sets of Kew magnetic self-recording instruments 
have been set up in the United States of America, at Washington and at Los Angeles, 
and the first Report from Washington, which has just been published and gives a 
record of work done in 1889, is very satisfactory, and should stimulate older magnetic 
observatories to bring their results into a state in which they will be more useful than 
at present and to publish them. It is satisfactory to find that the scale values 
adopted at Washington are nearly the same as the scale values which have been 
adopted at St. Petersburg, Vienna, Wilhelmshaven, Kew, and some other magnetic 
observatories. The importance of adopting as nearly as possible the same scale values 
for the similar instruments at different observatories cannot be too strongly enforced 
in the interest of the study of terrestrial magnetism. 
An attempt has also been made to apply the Gaussian analysis to the simultaneous 
magnetic disturbances in order to discover the amount of change in the magnetic 
potential of the Earth, which would be sufficient to account for these sudden magnetic 
disturbances. 
The large increase in the number of magnetic observatories with self-recording 
instruments seemed to warrant this attempt, but great difficulty has been experienced 
because we have scarcely yet arrived at the state foreshadowed by Gauss fifty years 
ago, “ when trustworthy and complete observations from all parts of the Earth shall 
be obtained.” 
For the complete solution of the problem, we should require records from Africa, 
from the continents of North and South America, and from Siberia, similar to those 
which are already obtained in Europe and Asia. 
In order to obtain some fair approximation to the changes of magnetic potential, 
necessary to give rise to the magnetic disturbances, I have collected photographic 
records of the traces given by the self-recording instruments for June 24th and 25th, 
1885, and for other more recent storms, from the observatories whose positions are 
given in Table II. 
The following tables give (1) the positions of these observatories, (2) the absolute 
values of the magnetic elements, (3) the comparative scale-values of the self-recording 
instruments for June 24th, 1885, as far as it has been possible to arrive at them ; 
(4) the values, in metric units, of certain magnetic disturbances. From these it will 
