
TRANSACTIONS OF THE SECTIONS. 3 
down the trunk into the ground, splitting the tree in two by a rent throughout the 
whole of its thickness. Lord Dufferin was so good as to have the tree cut down 
for examination. From a section of the upper branches it was obvious that the 
lightning had not entered at the top and passed through the branches into the trunk. 
Several workmen, indeed, in the neighbourhood saw the lightning-bolt moving hori- 
zontally before it struck the tree, .a fact entirely confirmed by the effect which it 
produced. The force of the bolt must have been great, as it was expended in tears 
ing off the piece of the trunk already mentioned, and in rending the tree in two, 
without separating the two halves. 
The track of the lightning was marked, from its point of entrance to its passage 
into the earth, by a darkish brown band, about 2 or 3 inches broad. A portion ot 
the wood thus marked will be sent by Lord Dufferin to Dr. Andrews, who will 
ascertain if the colouring matter contains any of those mineral substances which 
M. Fusinieri, an Italian philosopher, has found to exist in those parts of bodies over 
which lightning has passed. 
The fact contained in this notice, that an object may be struck by lightning in a 
locality where there are numerous conducting points more elevated than itself, shows 
that a lightning-bolt cannot be diverted from its course by conductors, and that 
the protection of a building from this species of meteor can only be effected by con- 
ductors stretching out in all directions. 

Account ofa Case of Vision without Retina. 
By Sit Davin Brewster, KH, D.C.L., F.R.S. § V.P.R.S. Edinb. 
In the course of last summer I met with a gentleman who had a peculiarity or 
vision of a very remarkable kind, and one of which I believe there is no other ex- 
ample. While hunting he fell from his horse, and received such a severe blow upon 
his head as to deprive him entirely of the sight of one eye, and to a great extent of 
the sight of the other. Neither of the eyes had suffered the slightest local injury 
from the blow, and therefore the total blindness in one eye and the partial blindness 
in the other arose from the insensibility of the retina caused by the disorganization 
of the part of the brain more immediately connected with the origin of the optic 
nerves. 
The degree of vision which remained in one eye was such as to enable its pos- 
sessor to recognise any friend at the distance of 400 or 500 yards, or more generally 
speaking, at a considerable distance; but in society he could not recognise his most 
intimate acquaintances. He could see only the nose, the eye, or the mouth of his 
friend; and he was not able to obtain, from the duration of the impression of light, 
and the rapid transference of his eye from one feature to another, such a combina- 
tion of the separate impressions as to give the likeness which they composed. 
_ In order to explain this singular result, I must recall the attention of the Section 
to a notice printed in the Reports of a former meeting of the Association, ‘On the 
Visual Impressions on the Foramen Centrale of the Retina*.’ 
From these facts it is obvious that the limited vision which we have described, 
was performed entirely on the choroid coat and through the foramen centrale of the 
retina. 
In order to ascertain the area of distinct vision, I requested the patient to tell me 
the number of letters he could read distinctly, and found that the angle which these 
letters subtended at the retina was as nearly as could be ascertained about 43 degrees, 
the angle subtended by the foramen as deduced from the previous experiments which 
I have mentioned. 
The use of the RuTINA is to give sensitiveness, and of the cHoro1D, distinctness. 
On the Form of Images produced by Lenses and Mirrors of different sizes. 
By Sir Davin Brewster, K.H., D.C.L., F.R.S., § V.P.RS. Edinb. 
The shape of the images of objects as formed by lenses and mirrors with spherical 
surfaces, has been treated of by various optical writerst ; but I am not aware that 
_* See Reports of the Association for 1848. 
7 Smith’s “ Complete System of Optics,” vol. i. chap. xii. p. 238, and vol. ii. Remarks, p. 83. 
1* 
