THE 
LONDON AND EDINBURGH 
PHILOSOPHICAL MAGAZINE 
AND 
JOURNAL OF SCIENCE. 
^ 
[THIRD SERIES.] 
APRIL 1840. 
XLIV. Letter from M. Kreil, Director of the Observatory 
at Mila?i, to M. Kupffer, Director General of the Phy- 
sical Observatories in Russia^ contaming a succmct Accou?it 
of the principal Results of VI. Kreil’s Magnetic Observa^ 
lions at MilanJ^ Communicated by Major Sabine, R,A. 
''T^HE observations arrange themselves under three heads: 
i. e. absolute observations, observations of the periodical 
changes, and of the perturbations of the magnetic forces. 
The absolute observations have shown that a correction must 
be applied to the declinations previously published, which 
had been determined within the confines of the Palace of 
Brera, where the Astronomical Observatory is placed, and 
where masses of'iron appear to have exercised a disturbing 
influence. A series of observations made last spring in an 
open meadow 640 metres from the observatory, showed that 
the previous determinations were 23' 16" in excess. A se- 
cond series made in the botanical garden adjoining the ob- 
servatory, on a spot which is 47 metres from the palace, but 
which was not available before, gave an error of 21' 51". I 
have taken the mean of these determinations, i. e. 22' 33"*5, as 
the quantity by which all the declinations hitherto published 
are to be diminished. 
The apparatus employed in these observations was made 
in Gottingen by M. Meyerstein, and is furnished with two 
needles, similar in form and weight, but of unequal magnetism. 
Under circumstances precisely similar, one of them (No. 4.) 
makes a vibration in 25"*2; the other (No. XVII.) in 29"*6. 
* From the Bulletin Scientijlque puhlie par V Acad. Bnp), des Sciences de 
St, Petersbourg^ vol. v. No. 21. 
Phil. Mag. S. 3. Vol. 16. No. 103. April 1840. R 
