+ 
36 
2 
NA TERE 
[JuLy 3. 1902 
such rays from two stations, and checked by rays from photo- 
graphs taken at a third station when the original intersections 
are not good or the identification of points doubtful. 
When the positions on a ground plan have been fixed and 
horizontal distances from the different stations have become 
known, altitudes of points above or below the station can be 
ascertained by observing the position of the points on the 
picture and substituting values in a simple formula 2 = d tana, 
where is the height required, @ is distance from the station 
ie 
5 
Fic. 1.—View from roof of Drummond’s Pank overlooking Trafalgar 
Square. 
point for the particular photograph under observation and tan a 
—, where x and y are abscissee on the principal 
INE 
horizontal and vertical lines as rectangular coordinate axes and 
f is focal distance for the picture. The practical working of 
this method of plotting horizontal intersections for obtaining a 
ground plan and then computing altitudes was illustrated by 
reference to a series of survey photographs from the south and 
Fic. 2.—View from corner of roof of Union Club overlooking Trafalgar 
Square. 
Peck ats ¢ = 
west sides of Trafalgar Square, looking north-east and east, and 
a plan of the square and neighbourhood on which horizontal 
traces of the picture planes were drawn. It was explained how 
in practice the horizontal distances of points from the principal 
vertical line of a photograph are first set off on narrow strips of 
paper, which are then transferred to the picture traces on the 
plan and direction lines set off from the station points through 
the selected points on the strips, when in all cases the direction 
NO. 1705, VOL. 66 | 
| honore prosecutze sunt 
lines would pass through the corresponding points on the ground 
plan of Trafalgar Square and the visible region round. It was 
also explained how to compute the height of St. Martin’s Church 
from the pictures. 
Two of the pictures used for illustration are here reproduced. 
It will be seen that these pictures bear some markings on their 
faces which are not usually found on ordinary photographic 
| pictures. 
(1) The horizontal line right across the picture is the horizon 
line, which marks the trace of the horizon plane of the lens (or 
station). It contains the principal axis of the lens. 
(2) The vertical line is the trace of the principal vertical 
plane, which also contains the principal axis of the lens and the 
station point. 
(3) The intersection of (1) and (2) is the centre or principal 
point of the picture perspective. 
(4) The scale at the top is part of a compass scale, and serves 
to show the magnetic orientation of the principal axis of the 
view, the vertical line serving as index. 
(5) The scale immediately below, which stretches as a band 
across the picture, is a scale of reduced horizontal angles (a 
tangent scale to a great circle of a sphere of radius equal to the 
exact working focal length). 
The MS. notes in the corners are memoranda originally noted 
on slips of celluloid by the photographer and put in place in 
special carriers before each picture was taken. All these mark- 
ings were printed as latent images at the same time exactly and 
by the same exposure as the picture. 
It was explained how all these markings were accurately 
obtained by aid of a simple mechanism specially designed by the 
author, who is responsible for introducing the system of re- 
cording automatically on the picture face information necessary 
for interpreting the picture, and how by aid of this information 
practical photo-surveying, which used to be often difficult, has 
become very easy and much more certain and accurate than 
formerly. The apparatus specially designed by the author and 
used for obtaining these pictures was shown and explained in 
some detail. 
The lecturer concluded by expressing a hope that in due time 
a simple standard type of working camera, fitted with a good 
lens and accurate recording mechanism (which could be easily 
removed and replaced at will), would find its way into general 
favour, and that regular libraries of standard readable pictures 
of interesting objects would come into existence. 
UNIVERSITY AND EDUCATIONAL 
INTELLIGENCE. 
Oxrorp.—The following is the text of the speeches delivered 
by Prof. Love in presenting Dr. W. H. M. Christie, C.B., 
| F.R.S., Astronomer Royal, and Dr. A. W. Riicker, F.R.S., 
Principal of the University of London, for the Degrees of D.Sc. 
honors causa, at the Encenia, on June 24. 
Inter mathematicos, qui Cantabrigiz quattuor et triginta 
abhinc annos graduati sunt, clarum erat nomen Willelmi 
Henrici Mahoney Christie, nunc inter omnes omnium gentium 
astronomos clarissimum, Astronomorum profecto ille annus 
magno proventu floruit cum in eodem Tripode Georgii Darwin 
nomen contineatur. Ambo hi viri Collegii Sancta Trinitatis 
socii creati sunt, sed in astrorum scientia alter alteram insistebat 
viam. Ille solis stellarumque soli parentium ultimam vetustatem 
investigabat : hic noster se negotio utiliori dedit ut solis stel- 
larum siderumque omnium et locos qui nunc sunt et motus ac- 
curatissime notaret. In hoc opere tantam peritiam adeptus est 
ut iam viginti abhinc annos et Astronomus Regius et Societatis 
Regalis Sodalis crearetur. Hoc gubernante fere omnia in 
| Observatorio Regio maximo vel novata vel in melius mutata : 
neque enim id solum curavit ut novis instrumentis cederent 
vetera, sed ut eadem paullo immutata idonea fierent ad sidera 
observanda observationesque ita factas memorize tradendas 
quemadmodum iubent astronomi recentiores. Ita vir peritis- 
simus et rem felicissime navavit et erario publico pepercit. 
Summa cius in rem publicam merita agnovit Regina nostra 
Victoria que eum titulo Comitis de Balneo ornavit: insigni 
Academie Parisensis Petropolitana 
alizeque complures quae eum inter externos litterarum commercio 
sibi adiunctos receperunt. Huius nomine inter Doctores 
nostros inscripto monstrabit profecto Academia nostra se 
