BY PROFESSOr. E. G. HOGG, M.A. 87 



according to the spot at which the instruments are set up. 

 It may be added, that highly magnetic greenstone occurs 

 on the summit of Mount Wehington. Our sites of 

 observation have obviously been chosen so as to avoid? as 

 far as possible, proximity to volcanic masses known or 

 suspected to be magnetic. 



At each of the selected stations we propose to deter- 

 mine, in absolute measure, the declination, dip, and 

 horizontal magnetic intensity. These quantities being 

 knoAvnfor ten places, well distributed over the Island, we 

 shall be in a position to construct a rough magnetic map 

 of the country, On which the iso-magnetic lines Avill be 

 shown. This map, as a first approximation, Avill not allow 

 for the abnormal magnetic phenomena introduced by the 

 greenstone and basalt : the determination of the local 

 abnormalities so introduced must be left to some future 

 time. The variation of the magnetic elements is of not 

 less scientific interest than the determination of the 

 absolute values of the elements themselves, at any given 

 date. To ascertain the variation, it Avill be necessary 

 to redetermine, after an interval of a few years, the 

 magnetic elements at the stations previously employed ; 

 and to properly efiect this, it is necessary that the sites 

 of observation should be suitably marked, so that future 

 observers may have no difficulty in picking them up. 

 The erection of permanent marks, such as are employed 

 in all important geodetic operations, appears, to Pro- 

 fessor M'Aulay and myself, to be so important that we 

 have laid before the present Government of the Colony 

 an application for a grant of £150, to defray the cost of 

 their erection and other incidental expenses incurred in 

 the survey. In the event of this grant of the public 

 moneys being made, we propose that the work of the 

 survey should be carried out in co-operation with the 

 Surveyor-General's Dei)artment. We are assured of 

 the cordial assistance of the Surveyor-General in all 

 matters connected Avith the survey. 



At the selected stations of observation we propose to 

 mark out the true geograpiiical meridian, and, when the 

 stations are suitable, to determine the bearings relative 

 to the site of observation, of any prominent landmarks 

 in view. The information so acquired may be of value 

 in supplementing that already acquired for the purpose 



