( ^< 53 . ) 
Art. XXIV . — Notice respecting Professor Han Steen's Chart 
of the Variation and Dip (fthe Needle. 
X' HE chart of the variation and dip of the magnetic needle 
which accompanies this Number, and which is marked Plate IV, 
was drawn by Professor Hansteen from the numerous tables of 
the declination and inclination of the needle which are given in 
his work on the Magnetism of the Earth, of which we have al- 
ready presented an analysis to our readers. This chart occu- 
pies two separate plates in Hansteen’s Magnetic Atlas ; but we 
have thought it preferable to unite both in one, in order that 
the relation of the lines of Variation and Dip maybe at once vi- 
sible to the eye. 
The Lines of Equal Variation are projected from observations 
reduced to the year 1787, whereas the lines of equal dip are 
projected from observations reduced to the year 1780. 
In the original chart published by Hansteen, he makes the 
magnetic equator cut the terrestrial equator only twice^ viz. in 
108° of West, and 21° of East Longitude * ; but in his letter 
to our correspondent M. Eumker, of which we have already 
availed ourselves in this Number, he states, that his own chart 
is in this respect erroneous, and that the Magnetic Equator ac^ 
tudlly crosses the terrestrial equator four times^ viz. in 25° of 
East, and 108°, 125°, and 170° of West Longitude, — a cor- 
rection which we have carefully made in the accompanying 
chart, altering, at the same time, the adjacent lines of 10°, 20° 
and 30° of North and South Dip, which must necessarily follow 
the inflexions of the Magnetic Equator. 
The Western Line (f' No Variation, which is more strongly 
marked than the rest, and passes along the Atlantic, and to the 
west of Hudson’s Bay, corresponds, very nearly, with the same 
line on the chart after Churchman, which we have already men- 
* In, the chart of the variation and dip, principally from Churchman, and re- 
duced to 17'94, published by Dr Thomas Young, and forming Plate 43d of his 
Elements of Natitral Philosophy^ vol. i. the Magnetic Equator cuts the real Equa- 
tor only twice, in 170° of West and 15° of East Longitude, 
