Vision and work / by Freeland Fergus.
- Fergus, A. Freeland (Andrew Freeland), 1858-1932
- Date:
- 1907
Licence: In copyright
Credit: Vision and work / by Freeland Fergus. Source: Wellcome Collection.
Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)
5/11
![[From the Proceedings of the Royal Philosophical Society of Glasgow.] Vision and Work. By Freeland Fergus, M.D., F.R.S.E., Hon Secretary of the Society. [Read before the Society, 13th March, 1907.] Sight is generally stated to be one of the five senses ; the others being hearing, tasting, touching, and smelling, but a moment's reflection suffices to show what is well recognised by all physiolo- gists, that the sense of sight is complex. It is a sense which responds only to very short vibrations in the luminiferous ether, and, if we exclude radio active emanations, such as the Rontgen rays, cannot be excited in any other known way. It conveys to us information as regards first, the form of objects; second, the colour of objects; third, the shade of objects; fourth, the posi- tions which they occupy in space relatively to each other; fifth, it is the factor which helps us to determine the apparent size of objects. The functions which concern us in the present com- munication are the first, third, and fourth. The Form Sense is usually and very conveniently measured by test types. The types commonly employed in this country are those which we owe to Professor Snellen, of Utrecht and so long as they are regarded merely as a comparative test, and not as an absolute standard, they serve the purpose admirably. To the form sense the term Visual Acuteness is commonly and we venture to think, somewhat erroneously applied. This function of vision is strictly limited in extent to that part of the field of vision which is associated with the macula lutea. The truth of this observation is easily proved by looking at an ordinary line of print. If the observer fixes his eye on a word about the centre of a line of printing, he will find, that so long as he fixes his eye on the word selected, he is quite unable to distinguish the words on either side of it. Or again, if the observer looks steadily at one of the lines of Snellen's types, he will observe that so long as he con- centrates his fixation on one of the letters, he is quite unable to see the others in the same line. This is specially true for those lines which contain the smallest characters. If one of the two letters which should be seen at 36 metres by a healthy eye is](https://iiif.wellcomecollection.org/image/b21639176_0007.jp2/full/800%2C/0/default.jpg)
