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I have given the name “Spasms’’ to these little motions. These 
appear as broadenings of the curves of the Bifilar-Magnetometer, 
which may be caused by vibrations of the magnetic force with an 
amplitude of from 3 to 15 g. (g = 0.00001 C.G.S.) during about 
1 to 8 minutes. On the scale of the bifilar-magnetogram 1 m.m. 
represents 4 minutes and 5 g. 
On trying to find an answer to the question, whether there is 
really evidence of a new kind of small disturbances, I employed 
two methods, that of statistics and that of direct observation. 
After the example of ESCHENHAGEN I constructed a Microvario- 
meter for the Horizontal Intensity, in which a light magnet is 
held perpendicular to the magnetic meridian by the torsion of a 
German-silver wire. The period of a compiete vibration was 9 seconds, 
the damping ratio 2—7, the value of the tenths of divisions, which 
could be estimated very easily, 0,06 g. 
With this instrument I observed continuously during one or 
two hours for many nights, and often took readings every fifth 
second, but unfortunately I have not yet been lucky enough to 
observe an undoubted Spasm. It occurred on only one occasion 
and was even then not a striking one. 
Notwithstanding this adversity I have been able to learn much 
from these observations. 
For instance I happened to be behind the telescope when a series 
of faint earth-waves, distinctly registered by the Seismograph, passed 
Batavia, and though wholly unconscious of this, I nevertheless 
noted three times horizontal and vertical motions of the magnetic 
needle. Their period was 2,5 seconds, half that of the free vibration 
of the magnet. 
This observation during the occurrence of a Spasm in the Mag- 
netogram indicated that really a kind of miniature disturbance had 
passed, and not a prolonged motion, caused by an earthquake. On 
one occasion I noted, while everything else was quiet, a strong 
impulse three times in one minute, which caused deviations of 20 to 
40 eo. The Magnetograms did not show the least signs of these, as 
the damping of the magnet is too rapid and the paper is not sensi- 
tive enough to light. Although my direct observations have not: 
until now met with much success, they nevertheless make the 
existence of very small magnetic disturbances appear probable in 
this case. Here at Batavia only the curves of the Horizontal Intensity 
show the Spasms, never those of the Declination which rarely 
exhibit perturbations at our tropical station. 
In compiling the statistics we met with three difficulties: 
