350 Proceedings of the Royal Society 
aerial screw differs widely from the aerial screws at present in use* 
and from the screw propeller employed in navigation, inasmuch 
as it is moveable in all its parts, and adjusts itself to its work in 
such a manner as to secure the maximum of elevating and pro- 
pelling power, with a minimum of slip. The screw propeller and 
aerial screws as at present employed are, on the contrary, rigid 
and unyielding , and possess no accommodating power. As a con- 
sequence, much propulsive power is sacrificed in slip. 
If the blades of the aerial screw referred to be greatly diminished 
in size, and formed of carefully tapered, finely graduated steel 
plate, it operates with remarkable efficiency in water, the elasticity 
of the screw diminishing the slip, while it greatly augments the 
propelling power. 
The following Gentlemen were admitted Fellows of the 
Society : — 
Rev. Thomas M. Lindsay, M.A. 
William Robertson Smith, M.A. 
Stair Agnew, Esq. 
Monday , 30 tli January 1871. 
Professor KELLAND, Vice-President, in the Chair. 
At the request of the Council, Dr J. Collingwood Bruce 
delivered an Address on “ The Besults of the More Decent 
Excavations on the Line of the Roman Wall in the North 
of England.” 
Nearly a century after Julius Caesar had landed in this island 
the conquest of Britain was begun in earnest. 
In the year 79 Agricola planted the Eagles of Rome on the banks 
of the Tyne, and during the next campaign carried his conquests 
as far as the Tay. Before he gave up his command, he had raised 
the Roman standard in the Orkney Islands. 
When Rome planted her foot she usually planted it firmly, and 
thus she retained in her grasp all the best portions of the island 
for more than 300 years. Some of the legions which landed in-tbe 
