184 Proceedings of the Boyal Society 
of Phladda lighthouse and north of MacArthur’s Head lighthouse, 
as the wave motion is described by the lightkeepers at these stations 
to have come in these directions ; and having no less than five 
observations of time by lightkeepers, and seven trustworthy 
observations from other places, I have been enabled to determine 
the following results, as to what may be held to have been the 
velocity of transit of the earthquake wave, the time at the source 
being taken as 5.40 p.m. (Greenwich), which assumes that the 
wave travelled from the source to Phladda at a velocity of 6.74 
miles per minute, which is the average velocity over the sea, and 
the distance from Phladda to the source being only 13 miles, any 
difference between this assumed velocity and the actual velocity 
will only affect the general result to a very small extent. 
It appears, then, from this table, that the velocity has varied from 
3*75 geographical miles per minute to 7*5 miles per minute in 
different directions from the source, the greater velocities being over 
the sea, probably due to the fact that in these directions the crust 
of the earth is thinner and lighter, and consequently more easily 
thrown into vibration. Thus the average velocity on sea journeys, 
was 6*74 miles per minute, and on land journeys, 4*65 miles per 
minute, the mean of the whole being about 5 J miles per minute. 
On the Chart the dotted line shows roughly the limit or range of the 
earthquake landwards, in so far as I have been enabled to ascertain it, 
and it will be seen that the earthquake wave was apparently propa- 
gated farthest in directions over the sea-basin, the wave being more 
quickly dissipated by passing over the land with its mountain chains. 
It is interesting to notice, that of the fourteen observers within 
a radius of 38 miles from the source who felt the shock thirteen of 
them mention having heard a noise, and no observers in Scotland, 
at greater distances, mention noise as an accompaniment of the 
earthquake. The stations where the noise was heard were for the 
most part situated on hard dense rocks, with little or no soil near 
them. 
The average duration of the disturbance for observers within a 
38 mile radius from the source is 4*4 seconds. 
The most of the reports received from Ireland by newspaper 
notices or otherwise I had no means of personally investigating : ; 
but all of them, as will be seen in the tabular statement, give the 
