In my previous post I mentioned Sir John Franklin’s doomed expedition to the Canadian Arctic, on which the HM ships Erebus and Terror tragically disappeared with all 129 men on board after the summer of 1845.
While we wait and see what Canada’s renewed rescue efforts might discover about Franklin’s last journey, I think there are some items from his more successful voyages in the Science Museum’s stores that deserve a closer look.
One such object is a variation compass and magnetometer, which would have helped determine a true course in relation to the magnetic and geographic norths (which do not coincide, as you may know), as well as measuring the intensity of the earth’s magnetic forces at different points at sea. Apparently used by Franklin on some of his Arctic voyages, it was later also used by others looking for the man among the ice!
To complete my imaginary trek from pole to pole, I also found a Robinson dip circle taken to the other extreme of the globe by Sir James Clark Ross, on board HMS Terror, of all vessels.
After a string of successful expeditions up north, Ross set off on a magnetic survey mission to circumnavigate Antarctica between 1839 and 1843.
The magnetic needle of the dip circle, resting on the pivot at the centre of its case, would align itself to the Earth’s magnetic field, so the angle it made with the horizontal plane could be read off the graduated frame – this was of particular interest in polar regions, where the downward pull is the greatest, and where navigation with other instruments proved more difficult.
And to think that all this mileage is now under one roof…