The motive power was india-rubber in the condition of torsion; the propeller, a screw.
Sigsbee's small water-bottle on the double valve principle actuated by a propeller requires extremely skilful handling to enable it to give good results.
The "Thetis" propeller fouled a net laid at the entrance to the harbour and carried it with her.
Later apparatus, such as Pettersson's bifilar current-meter or his more recent electric-photographic apparatus, and Nansen and Ekman's propeller current-meter, measure both the direction and the velocity at any moderate depth from an anchored vessel.
" The wing, both when at rest and when in motion, may not inaptly be compared to the blade of an ordinary screw propeller as employed in navigation.