9 
railway. Thence it makes straight for the fortified hill of 
Llanamynech, its line coinciding with the high road. On 
reaching the summit of Llanamynech it takes the western 
or Welsh side of the two large camps, and passes down into 
the valley to the south of Whitehaven, which was the limit 
of our expedition. The results of our examination are 
the direct proof that the dyke was made for military 
purposes and that it took the line which was best adapted 
for repelling the incursions of the Welsh. Throughout the 
district which was examined the embankment faces Wales, 
and was therefore made to defend the country within it 
from the Welsh. Dr. Wright’s view, therefore, that it was 
a mere geographical boundary to prevent the Welsh from 
stealing the cattle of the Mercians cannot be maintained, 
although it may perhaps receive some confirmation from 
the nursery-legend of Taffy. The camps in the neighbour- 
hood of the dyke are probably older than Ofia’s time. The 
bronze spears found in Llanamynech imply that the camp is 
not later than the Bronze Age, while the Roman coins in 
that of the Breiddan point to its occupation by the Romans. 
“ On the Action of Sulphuric Acid on Diallyl,” by 
William Robert Jekyll, Dalton Chemical Scholar in 
Owens College. Communicated by Professor Roscoe, F.R.S. 
Diallyl was first prepared by Berthelot and Luca in 1856. 
They found that it dissolves in concentrated sulphuric acid 
with the evolution of much heat, and that after some hours 
an oil separates, which appears to be modified hydrocarbon. 
In 1866 Schorlemmer published a paper on a new series 
of hydi’ocarbons derived from coal tar, having the formula 
(C„H 2n _„)2 (Proc. Roy. Soc. xv. 132). He there says, “ As 
these hydrocarbons were obtained by the action ol sulphuric 
acid on coal tar oils boiling below 120° and as they differ by 
C 2 H 4 , it appears to me almost certain that they are polymers 
of the hydrocarbons of the acetylene series formed 
