being produced by them. It was also felt strongly in the mines at Reefton. In order to obtain some idea of its depth I tried Professor Milne's method of co-ordinates, but without success. As each of the simultaneous equations is more or less inaccurate, different results are obtained by combining them in different ways, and I found, after many attempts, that these results for velocity of transit and depth of centrum were so discordant that I lost all confidence in them. The method is a very good one when the data are sufficiently accurate; but it is not adapted for obtaining the most probable result from a mass of incorrect data.

We have seen that the effects of the shock were most severe in the neighbourhood of Glynn Wye, so that probably the angle of emergence was here between 45° and 55°, and this, with the epicentrum situated sixteen miles away, would give the depth of the centrum between sixteen and twenty-three miles. When we have discussed the velocity of propagation we shall be able to make another approximation to the position of the centre of the centrum.