] 
q 
d 
] 
: 
AND INSTRUMENTS AT MUNICH. 505 
influence), is a question on which there may be different 
opinions. 
If the atmospheric conditions which modify the influence of 
the sun’s rays on the earth’s surface, such as direction of wind, 
clouds, &c., have also a decided influence on the magnetic devi- 
ations of ordinary occurrence,—and if the extraordinary disturb- 
ances are in many respects in exact connexion with the times 
of the day and of the year, (as appears to result from the ob- 
servations of this observatory,) it seems to me that we have no 
remaining reason for seeking other sources of magnetic varia- 
tions than the sun*. Assuming this view to be correct, there 
would be no doubt under which of the two aboye-named classes 
of phenomena the manifestations of terrestrial magnetism should 
be ranged. 
M. Gauss has recently subjected to exact observation a 
highly remarkable feature of terrestrial magnetism, i. e. the 
simultaneity of magnetic variations at different points of the 
earth’s surface. Observations have not determined how we 
should represent to ourselves this simultaneity. It seems most 
agreeable to natural analogy to view it as resembling the propa- 
gation of atmospheric changes which prevail over districts of 
greater or less extent, advance with a rapidity proportioned to 
| their magnitude (or intensity), and suffer various modifications 
_ during their progress; but with this difference, that magnetic 
variations pass over great spaces in hardly an appreciable inter- 
val of time, and suffer smaller modifications in their passage 
than any other meteorological phenomenon with which we are 
acquainted. Observations, at the northern extremity of Europe, 
and at remoter stations, have however now shown that the vari- 
ations are modified, and that to such a degree that at last the 
similarity entirely disappears. If the supposition already men- 
tioned, that a// magnetic changes are connected with periods of 
the day or year, be correct, it is manifest that no strict simul- 
* On examining the great number of disturbance observations recorded in 
our registers, it is seen that when a disturbance occurs during the day the de- 
clination needle makes an oscillation towards the west; if the disturbance is 
during the night, the movement of the needle is towards the north. Our obser- 
vations, in accordance with determinations elsewhere, show moreover that the 
more or less frequent occurrence of disturbances and their magnitude, are in 
eonnexion with the times of the day and year. If great and irregular move- 
ments of the needle take place during auroras, we have no reason to assume 
the aurora to be the acting force: it may with more probability be regarded 
merely as an accompanying phenomenon. 
VOL. III. PART XI. ot, 
