BEITISII ISLES FOE THE EPOCH JANUAEY 1, 1915. 
71 
who will carry out the work, several matters of importance suggested to me by the 
experience of the present re-survey. 
(1) The enormous a-dvantages that the re-survey has enjoyed from association 
with the Ordnance Survey Office has impressed me very much. The stations are 
permanently marked and the co-ordinates and azimuths determined. They can 
be recovered at any time by, and only by, the O.S.O. No private individual or 
scientific society could arrange for this with the same degree of rapidity or efficiency. 
It is an almost obvious conclusion that the further magnetic survey of the British 
Isles should be handed over to the Ordnance Survey Department as a definite 
part of the general survey of the Kingdom. Moreover, the present re-survey, in 
conjunction with that of Rucker and Thorpe, provides a very good basis from 
which to work ; so that it appears to me that, instead of leaving over the next 
re-survey for 10 or 15 years, it would be better to arrange for a continuous revision 
of the magnetic data, to be carried on by the officers of the Ordnance Survey 
concurrently with the regular scheme of revision of the general survey as arranged 
by that Department of the Public Service. 
I take this opportunity of drawing attention to the excellence of the magnetic 
charts in this volume which have been prepared by the Ordnance Survey Office from 
my original drawings. r 
(2) While the present arrangement of stations gives results of great value, the 
stations are not selected on any systematic scheme. I hope that as opportunity 
occurs some of the older stations may be abandoned and new stations determined, 
so as to bring the general scheme into some definite geometrical order. While I do 
not advocate any large increase in the number of stations, there are clear indications 
of localities where observations at a few additional properly selected points Avould 
greatly simplify the elucidation of the phenomena. Further, there are obvious 
lacunae where new observational stations should be chosen. 
In this connexion it is important to ascertain if a station is really representative 
of a moderately extensive area. The manner of testing this is properly included 
under the next main point. 
(3) Magnetic surveying by the use of absolute instruments appears to me to 
be unnecessarily cumbrous and not conducive to the best results. Further, no 
standard of magnetic force exists at present by which instruments can be compared 
with an accuracy of ly. It thus seems desirable that a standard should be ’Prepared 
in terms of the electrical standards of the country. 
In the ‘ Roy. Soc. Proc.,’ A, vol. 92, p. 313, 1916, I have given the results obtained 
in Ireland by means of a portable magnetometer which gives by a single direct reading 
the horizontal force at any station referred to a standard base value. The success 
attained by this method justifies a serious attempt to improve the instrument, so that 
two horizontal components at right angles can be measured, and further, to apply 
