426 REPORT—1899. 
clearly ; it may be of flag-stones, concrete, or light-coloured bricks. Its 
curb, or edge, towards the camera must be sharp and clearly visible, 
because it is an important line of reference in the photograph. The 
wall should be painted of a light colour—bluish, not yellow. Fifteen 
small marks, each the size of a sixpence, arranged in three horizontal and 
five vertical rows, at the exact distance of 3 feet apart, should be made 
upon the wall, to give a scale to the photograph. They are indicated in 
fig. 1 by small crosses. The lowermost row should be well clear of the 
pathway, say 1 foot above its level. Some of these marks will be sure to 
be visible in the photograph, though most of them will be hidden by the 
body of the horse. Simple screens or hangings should shield the horse 
from distracting sights. An aperture in a screen will enable a person 
who is stationed for the purpose on the other side of it to mo- 
mentarily arrest the attention of the animal when the photograph is 
about to be taken. The camera is to be firmly clamped to a solid stand 
opposite to where the horse is to be placed, and to remain undisturbed 
during the whole operation. Its object-glass is to be 5 feet above the 
ground, that the view from it of the pathway may not be too much fore- 
shortened, and it is to be 30 feet from the wall. The equivalent focus of 
the lens should not be less than 9 inches, otherwise the photograph will 
be too small for convenient measurement ; the lens used in the experiment 
was of 15 inches focus, with plates of 64 x 43 inches, and proved exactly 
suitable. ‘The most important point of all is that the plate-holder of the 
camera should be strictly parallel to the wall, as tested by the images of 
the marks on the wall forming squares of exactly equal sizes on its 
ground-glass focussing screen. As many of them as are visible in the 
photograph will, of course, do the same. A label should be fixed to the 
wall, well above the back of the horse, but within the field of the camera, 
on which the permanent data of the instalment should appear in bold 
letters, easily legible in the photograph. Lastly, the horse should wear a 
distinguishing number for after-identification. The photograph will thus 
bear internal evidence of the standard conditions having been observed, 
and will carry its own scale. An experiment succeeded perfectly of indi- 
cating the position of the prominence at the hip, which is easily to be felt 
but is not distinctly seen, by labelling it with a wafer of thin white paper 
the size of a shilling ; thick paste which penetrated between the hairs was 
needed to make the wafer adhere.- The mark was, however, unnecessarily 
large and conspicuous ; one of the size of a sixpence would have been ample, 
It might, perhaps, be printed on the horse with water-colour. The 
question whether any, or what, points of anatomical interest might be 
treated advantageously in this way has not yet been fully considered. 
Calculation from measurements on the Photograph.—Fig. 1 represents, 
on a scale of about one-third the actual size, the appearance of one of the 
photographs and of the measurements made upon it. SS is the line of 
junction between the pathway and the wall ; the little crosses indicate 
the positions of the marks already described ; qq is the curb, or edge, of 
the pathway opposite to the camera ; p is any desired point on the ridge 
of the back of the horse, whose height above the ground it is desired to 
find. A measurement is made of the line that falls perpendicularly from 
p to qq; also of that from 4 to gq, h being the point where the perpen- 
dicular from p cuts a line so drawn on the pathway as to touch the sides 
of the shoes of the fore and of the hind foot that are nearest to the 
camera, and which may be called the hoof line. | Practically, the simplest 
