623 
the compression, and the doubled-axis of the rotation, consequent 
on the displacement of each point through a space represented by /. 
Also it is easy to see that <] 2 <rds a pure vector. Hence 
S. < V <1 <r '= 0. 
If therefore there he two similar media , and the 'particles of one 
he slightly displaced in a continuous manner — the particles of the 
other being displaced through vectors proportional to the rotations 
at each point in the first mass — this displacement takes place with- 
out condensation . 
And, as Y. <1 <1 s = 0, we have the other result, that if the 
particles of the second medium he displaced through vectors repre- 
senting the direction and rate of most rapid change of compression 
in the first, such displacement will take place without rotation . 
But this is merely another way of stating the first proposition in 
IY. — (Compare Thomson, “ On a Mechanical Representation of Elec- 
tric, Magnetic, and Galvanic Forces” — Camb. and Dub. Math. 
Jour., vol. ii. ; and Maxwell, “ On Physical Lines of Force” — Phil. 
Mag., 1861-62.) 
The following Donations to the Library were announced : — 
Proceedings of the Royal Geographical Society of London. Vol. YI. 
No. 2. 8vo. — From the Society. 
Comptes Rendus for 1861. 4to. — From the Academy. 
The Cat-stane, Edinburghshire. Is it not the Tombstone of the 
Grandfather of Hengist and Horsa'? By Professor Simpson. 
8 vo. — From the Author. 
Antiquarian Notes of Syphilis in Scotland. By Professor Simpson. 
8vo. — From the Author. 
Quarterly Report of the Meteorological Society. January to 
March 1862. 8vo. — From the Society. 
Abstract of Proceedings of the Geological Society of London. No. 
81. — From the Society. 
