HoGBEN. — Oil tlic EartJiqiiakc of December 5, 1881. 465 



or lessened, this displaces the focus on the camera-screen only 

 by half that distance, and an adjustment of lin. on the tube 

 represents about 2iu. of difference in the camera. 



The eyepiece taking the place of the camera-screen is ad- 

 justed to the j)lane of the sensitive surface of the plate in the 

 dark slide, and is easily brought to as great a degree of exact- 

 ness as the dark slides themselves will register, and if needful 

 it may also be made to compensate any displacement of the 

 foci that may occur through using an imperfect telescopic eye- 

 piece. In using the screen eyepiece the picture should be first 

 arranged, and a proper balance of focus obtained; then, throw- 

 ing back or aside the screen, the eyepiece may be applied to 

 the production of focal sharpness, which may thus be made 

 as perfect as lies within the capacity of the lenses concerned 

 in its production. 



Such, so far, have been my experiments and discoveries, 

 and in bringing them and the instrument under the notice of 

 the Society I do so with a view to their publication, so that 

 others may have the opportunity of making improvements ou 

 what I have already effected, or of suggesting something en- 

 tirely new in its place. 



Ai;t. LIV. — The Determination of the Origin of the Ecirth- 

 quake of the 5th December, 1881, felt at ' Christchurch 

 and other Places. 



By Geoege Hogben, M.A. 



[Uea-'' before the Philosophical InsHtntc of Canterbury, 2rul October, 



1800.;} 



Plate XLI. 



I BEGAN to examine into the circumstances of this earthquake 

 in connection with the general work of determining the origins 

 of New Zealand earthquakes, and expected to find that the 

 source of the disturbance was situated beneath the surface of 

 the earth somewhere in the neighbourhood of Castle Hill, or 

 (as Professor Hutton suggested tome in conversation) between 

 Mount Torlesse and Mount Franklin. The evidence, however, 

 gives a different result, and yet I believe is sufficient to show 

 that the epicentrum is at or near the same spot as that of the 

 1st September, 1888. 



The facts on which the present notes are based are related 

 in the Lyttelton Times and Press of the following days. Very 

 full accounts are given, but the number of data exact enough 

 for our purpose is small. 

 30 



