# Physics explained — South!

> Chapter companion for South! by Ernest Shackleton.

## What happens

This chapter details the scientific observations and navigational methods employed during the Endurance expedition, focusing on the challenges of determining position in drifting pack ice, magnetic and atmospheric measurements, and the use of occultations to check chronometer accuracy.

## Themes in this chapter

### Scientific Inquiry and Practicality

The chapter details the adaptation of scientific methods to the harsh conditions of the ice, including magnetic measurements, atmospheric electric potential, and navigational techniques.

### Endurance and Perseverance

The crew continued systematic observations and navigation despite the ship's drift, extreme cold, and the loss of the Endurance.

## Character check-ins

### Frank Worsley

Constructed a drift vane apparatus to estimate the direction of ice drift.

### Ernest Shackleton

Leader of the expedition; his ship's drift and position were key to the scientific work described.

## Key lines

> During the drift of the Endurance both means of observation were generally employed. A comparison of the results showed an agreement between sextant and theodolite, within the errors of the instrument if the temperature was above about 20° F.

Both sextant and theodolite gave consistent readings above 20°F, but discrepancies arose at lower temperatures due to mirage.

_Highlights the practical challenges of celestial navigation in polar conditions._

> On June 24 a series of four occultations were observed; and the results of the observations showed an error in longitude of a whole degree.

Observing four occultations on June 24 revealed a one-degree error in the ship's calculated longitude.

_Demonstrates the critical role of occultations in correcting navigational errors._

> The drift was always to the left of the actual wind-direction. This effect is due to the rotation of the earth, a corresponding deviation to the right of the wind direction being noted by Nansen during the drift of the Fram.

The ice drifted left of the wind due to Earth's rotation, similar to Nansen's observations on the Fram.

_Connects the expedition's observations to broader geophysical principles._

## Links

- HTML: https://www.betterreads.online/discover/south_se/chapters/physics
- Book: https://www.betterreads.online/discover/south_se
- All chapters: https://www.betterreads.online/discover/south_se/chapters