TT -_s 
ON THE FACTS AND THEORY OF EARTHQUAKE PHENOMENA. 5 
the great Scandinavian chain, and is in fact nearly a normal to the actually 
observed directions of shock. 
It is a fact observed in many other seismic mountain chains, as well as 
along the lines of great valleys and river-courses, that the main directions 
of propagation of shock are along the lengths of the chains, valleys or river- 
courses; and a very obvious explanation why this should freguently be the 
ease suggests itself, namely, that the solid materials of the earth are Jess 
shattered and discontinuous, and more homogeneous in these directions 
than in those transverse to the ranges and valleys, &c.; but how far this is in 
any way connected in nature with Perrey’s conclusion admits still of doubt; 
and indeed it is manifest that any attempt to calculate a general or mean 
resultant, from the horizontal component of shock only, must be at least 
incomplete, and, from other reasons that will be given when treating of 
seismometric instruments, may be said to be at present impossible. I should 
by no means wish, however, altogether to reject this ingenious method of 
discussion in the present state of our knowledge. 
Perrey’s results are subjoined for— 
Taste IV.—Earthquakes of the British Islands and Northern Isles. 
Earthquakes with date of month. 
. = 
a 3 eto |S ss 
Sol psa Mate »|a}e1/ 31] 3 |2e] Tota. 
= ae | S| o|8)/es/]seisirne 
o g 5 o/s a 3 Sod | S) Olas 
EIS ISIE EIE/S Pl ES) S18 ES 
Pere Slss |S: | lo lols | A ee 
NS eg ee lee Bike Pie 8 
elte...|) 1 eae 1 1 2 ua 2 4 11 
TS Ae og fe ee i a ae elit BiGuth 46 
[2 ae i 1 1 aoe 1 4 
Ve. oo oe 1 Ve Se 1 
XVI. 1 Zales 1 2 1 1 8 
XVII. 3 eet ase 1 2 3 1 2 2 14 
XVIII.) 5 4 7 5 cy 2 3 5 6 6 8 8 1 63 
XIX. 9 9/10 7f 8 6 5} LI | 12 Sie ll ae 2 110 
Totals.| 21 | 16 | 19 | 16] 16] 10 ct (et Nl =e sl We fh vi A 234 
Poe Spring Summer Autumn 
5 
The number occurring in spring and summer together is but three-fourths 
that of autumn and winter united, the relative number for the four seasons 
being— 
MNItG ree oes Is k stmINS 8 -- 1°03 
Spring ...... dp Wasa Hees O76 
Summereege sf! 2.8 Sela hs VIO96 
AM ee Sols oak ee Ot 
And the two months of the critical epochs— 
Wintersolsticegiy. o2scl.c eee ek 1:28 
Spring equinox.........0000002020°96 
Summer solstice ....... ie eS O58 
Autumnal equinox ..........060.1°13 
