( 202 ) 
. . . 2, 
Two times the square of the smallest positive root of C («) 
2n 
is smaller than the smallest positive root of sf (x) increased by 1. | 
(x) 
: ee Qv—1 
Two times the square of the smallest positive root of C, oi 
is smaller than the smallest positive root of C (x) increased by 1. 
The two latter theorems furnish us with a less narrow limitation 
for the smallest positive root of the function C (x) than the theo- 
rem at the conclusion of § lL. 
Terrestrial magnetism. — Dr. W. van BEMMELEN. “ * Spasms” 
in the terrestrial magnetic force at Batavia.’ (Communicated 
by Prof. H. KAMERLINGH ONNES). 
(Read September 30th 1899). 
Since the great development of Seismology, the instruments, which 
record photographically the quantities determining the earth’s mag- 
netism have also rendered good service as Seismographs in the 
researches on the propagation of earth-waves in the surface of the earth. 
During half a year I had the opportunity of tracing the seismic 
disturbances in the Magnetograms at Batavia, and this under very 
favourable circumstances; for, not only was the fear of local distur- 
bance very small, the temperature constant and the damping large, 
but since June 1% 1898 a new Milne Seismograph had been working 
and furnishing accurate information about seismic disturbances. When 
an earthquake is near, these appear in the curves of the Magneto- 
grams as discontinuities, viz. the needle suddenly starts vibrating and 
continues doing so for some minutes; when at a greater distance, on 
the contrary, only a more or less considerable regular broadening of 
the curves appears. Comparison with the Milne-Seismograms quickly 
taught me that the seismic disturbances at Batavia seldom are large 
enough to appear in the Magnetograms, but also conversely, that 
no trace of a large number of analogous disturbances in the Mag- 
netograms could be detecied in the Seismograms. 
Hence there is danger of considerable confusion: if for instance an 
earth-wave has passed at Batavia at 11.10 which has not appeared in 
the Magnetograms, then very likely a non-seismic disturbance, occur- 
ring at 11.5 for instance, will be mistaken for an earth-wave and an 
error of minutes will be made. Moreover it is necessary to inquire 
whether a new phenomenon does not mingle with those just mentioned. 
