PRESIDENTIAL ADDRESS. oil 
large size, much slower than a topographical survey. It is often found 
advisable to take up the survey of the former somewhat irregularly, while 
it is important for the proper progress of the latter that it should be taken 
up regularly and methodically. The Ordnance Survey 1-inch map has, since 
1824, not had a separate survey of its own, but has been based on the 
cadastral survey. Ordnance Survey experience has shown that the delays 
in completing the topographical map, due to this course, have been much 
greater than one would have expected, and that there are grave dis- 
advantages in having the scale of survey very much larger than that of 
the finished map. These objections do not apply, or can be overcome, if 
the cadastral survey of any locality is completed before the topographical 
map is taken up. This is a condition not likely to be often fulfilled in 
the case of future topographical surveys. I advocate therefore that, follow- 
ing the general practice, there should be entirely separate topographical and 
- cadastral surveys. I should advocate this even where it is essential to 
keep the expense as low as possible. More economy would probably result 
from the adoption of a fairly small scale for the topographical map, from 
curtailing the small detail to be shown on it, and from showing on the 
cadastral maps only such detail as is needed for property purposes, than 
would result from making one survey do for both classes of maps. 
On the other hand I consider that, even when separate surveys are made 
for the two classes of maps, it is advantageous that both should be made 
under the same head. The more usual course is, however, to have the two 
surveys independent, and in some cases local circumstances may make the 
course I advocate inadvisable. 
Triangulation. 
The first preliminary to any survey should be a triangulation. It is the 
most satisfactory course, and the best economy in the long run, to carry 
out with the greatest accuracy possible the primary triangulation on which 
the survey is to be based. Such a triangulation will remain good for a 
very long period. For example, the primary triangulation of the Ordnance 
Survey was commenced in 1791; while some doubts have been expressed 
whether it is accurate enough to combine with other more recent work for 
the purpose of investigating the figure of the earth, no one has questioned 
that even the earliest part of this triangulation is amply accurate enough 
for map-making purposes. 
On the other hand I do not advocate carrying out a primary triangula- 
tion until arrangements have been made for basing a survey on it. In 
South Africa an excellent and very accurate primary triangulation has been 
carried out. This triangulation was undertaken largely no doubt for scientific 
purposes. While answering its purpose in that respect it has so far had 
no surveys of any great extent based on it. An accurate triangulation is 
now a much quicker and less expensive operation than it used to be. The 
introduction of Invar tapes and wires has largely expedited and simplified 
the accurate measurement of base lines, while the improvements effected in 
theodolites enable equal or greater accuracy to be obtained with the com- 
paratively small and handy instruments now made than could be got for- 
merly with large and cumbrous instruments, such as the 36-inch theodolites, 
with which most of the primary triangulation of Great Britain and Ireland 
was carried out. Unless observations are rendered difficult by numerous 
buildings, by trees or by a hazy or smoky atmosphere, a good primary 
triangulation should not now be very expensive. It is usual to base on 
the primary triangulation a minor triangulation of several orders, the object 
being to have an accurate framework of trigonometrical points on which 
to base the survey. If it is important to keep the expense low, the trigono- 
metrical points may be rather far apart, intermediate points being fixed by 
