« 748 
NATURE 
[JUNE 2, 1923 

the probabilities are that the strips of photographs that 
they produce will be badly curved and leave gaps 
between them, while the individual photos will be 
tilted up to about 6 degrees and taken from varying 
heights. In such circumstances accurate compila- 
tion is almost impossible unless a map already exists, 
and, even then, re-section and re-projection of individual 
photos will be necessary if anything but the roughest 
results are to be obtained. The gaps that have been 
left between strips will, moreover, have to be filled up ; 
and, as this is not an easy operation, several additional 
flights may be necessary for a satisfactory completion 
of the mosaic. 
We are, for these reasons, definitely of the opinion 
that to employ crews that are not specially prac- 
tised in the work is to court certain failure; at 
least in the earlier stages, before experience has been 
gained. 
Special equipment, such as gyro rudder controls, etc., 
is, in our opinion, necessary for continuous successful 
work at the rate we have indicated, namely 100 square 
miles a day. Should the gyros break down in the field, 
it would be possible to carry on for a time in the absence - 
of any gyroscopical aid, but the strain on the pilot 
would be so greatly increased that his work would 
deteriorate seriously unless he confined himself to 
considerably less work than we have indicated for a 
single flight. 
It is also important to use a stable aeroplane, having 
adequate accommodation for the observer and _ his 
camera and for the pilot’s special instruments. We 
have ourselves used a tractor (D.H. 9a), but we con- 
sider that a pusher would be far more satisfactory on 
account of the better view downwards, sideways, and 
forwards. 
SUMMARY. 
We have shown that it is possible to carry out aerial 
surveying by vertical photographs at the rate of 100 
ately flat country the results so obtained can be worked 
up into roo square mile mosaics which, when reduced 
to a suitable scale, will fit a true map within 100 yards 
at all points. If so desired these maps can be adjusted 
to fit any number of control points with very little 
extra labour. If these control points are spaced about 
10 miles apart, the absolute error of any point on the 
mosaic should be less than roo yards, but, if more 
closely spaced contro] points are available, the errors 
can be reduced, reaching a limit of something less than 
20 yards, when the spacing is reduced to one mile. 
If the available control points are spaced more 
widely than ro miles apart, a measure of control can 
be provided from the air by navigational methods. We 
estimate that, even when the control points are spaced 
so far apart as 50 miles, we could in this way control 
the position of the 100 square mile units within } to 4 
mile. We are working on this problem at present. 
The maps can be made throughout from contact 
prints off original negatives, no re-projection of indi- 
vidual photos being necessary. 
Triangulated points, forming any convenient pattern, 
can be used as control points; e.g. previously existing 
primary, or secondary, triangulations could be used. 
The methods are dependent on there being sufficient 
detail visible on the photos to allow them to be joined 
correctly ; they would not be practicable on absolutely 
featureless deserts or prairies. 
Specially trained, picked crews using suitable aero- 
planes, specially equipped, are necessary for success. 


Obituary. 
Cou, G. F. Pearson. 
() April 25, Col. George Falconer Pearson died at 
Kington, Herefordshire, aged ninety-six years- 
He was one of the last, if not the very last, of devoted 
servants of the Crown who joined the Indian service 
some time before the Mutiny, and became a dis- 
tinguished pioneer of systematic conservancy of the 
Indian forests. 
Pearson commenced his service in the 33rd Regiment 
of the Madras Light Infantry in 1846, in which he 
became adjutant, and he also acted for some time as 
A.D.C. to Sir Herbert Maddock. He happened to be 
on leave at home when the Mutiny broke out, but 
returned at once to India and joined his regiment in 
the Central Provinces, where he was employed in the 
chase of Tipoo Sahib and other rebels. After the 
Mutiny he raised a force of military police, 600 strong, 
with which he put down general lawlessness in the 
province. 
Having thus become well acquainted with the 
extensive forests and the various tribes living in and 
around them, Mr. Temple, the Chief Commissioner, 
appointed Pearson the first Conservator of Forests of 
the Central Provinces in 1860. Pearson, being endowed 
with an iron constitution and great energy, devoted 
the next eight years to the organisation and administra- 
NO. 2796, VOL. TIT] 
| tion of the 20,000 square miles of Government forests 
in the province, selecting and demarcating reserves, 
introducing a system of regulated utilisation, starting 
a successful method of protecting the forests against 
the annually recurring forest fires, and regulating 
shifting cultivation; in other words, substituting a 
regular system of management for the method of 
reckless devastation of the past. His success brought 
him the special thanks of the Government of India 
for his valuable services. 
In 1868 Pearson was transferred to the charge of the 
forests in the North-west Provinces, where he re- 
organised the department, estimated the yield capacity 
of the forests, and opened out the hill forests by the 
construction of roads, bridges, and timber slides, by 
which large quantities of timber were brought down 
to the plains for railway construction. In 1871 he 
was appointed to act for Dr. Brandis as Inspector- 
General of Forests, and in 1872 he left India to take 
up the appointment of director of studies to the British 
forest probationers at Nancy, a post which he held 
Kington, where he lived for thirty-nine years, being 
a J.P. and the friend of all classes of the inhabitants. 
energetically absorbed and utilised the leading principles 
of rational forest conservancy, and took a great part 

sq. miles to the day’s flying. When working in moder- — 
until 1884. On his final retirement he settled at — 
Pearson, though not specially educated as a forester, — 
: 
, 
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