THE 



LONDON AND EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



APRIL 1810. 



XLIV. Letter from M. Kreil, Director of the Ohservatory 

 at Milan, to M. Kupffer, Director General of the Phy- 

 sical Observatories in Russia, containing a succinct Account 

 of the 'principal Results ofM.. Kreil's Magnetic Observci' 

 tions at Milan.-^ Communicated by Major Sabine, R.A. 



THHE 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 w^as 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 Scienttfique j)ublie par PAcad. Inq^.. des Sciences de 

 St. Peler&hourg, vol. v. No. 21. 



Phil. Mag, S. 3. Vol. 16. No. 103. April 1840. R 



