Deep-Focus Earthquakes.

MR. F. J. SCRASE¹ has recently found confirmation of the great depth assigned to certain earthquakes by the late Prof. H. H. Turner by recognising, in the data of the International Seismological Summary, the two separate branches of PR₁ and SR₁ that are to be expected if the focus be deep, and by observing the substantial agreement of their travel-times with the expected times calculated on the basis of the Zoeppritz-Turner tables. It may be of value to note in this connexion that we may, by the use of these reflected pulses, arrive at what is certainly a minimum value of the depth of focus, and this independently of any previous travel-time tables and even of any error in the assumed time of origin. This would eliminate any objection that might possibly be made to the use of the Zoeppritz-Turner tables.