I therefore returned to the camp and helped Dovers take observations for longitude and magnetic variation.
Fog forms at one period of the magnetic variation, cloud at another.
magnetic variation charts are published by both the United States and British governments.
That is the magnetic variation, plus 14.8 minutes for those iron boxes, of this place at the present moment.
He took the "lay" of the place with a pocket-compass, allowing two seconds for magnetic variation.
Compasses are for convenience printed on the charts, and data given as to the magnetic variation and its rate of change.
The magnetic variation ascertained at this camp was 12 30′ east.
As the compass is a universal navigational instrument, information as to the magnetic variation is needed for the charts.
On these charts he set down lines connecting those localities at which the magnetic variation was identical.
The latitude, chronometric differences of longitude, and magnetic variation, were determined on shore at this southern point.