Volume 1

Observations on man, his frame, his duty, and his expectations. In two parts / By David Hartley.

  • Hartley, David, 1705-1757.
Date:
1749
Catalogue details

Licence: Public Domain Mark

Credit: Observations on man, his frame, his duty, and his expectations. In two parts / By David Hartley. Source: Wellcome Collection.

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252/552 (page 220)
One or both of thefe Ablions of Light feem to in- creafe the Secretion and Circulation of the aqueous Humour in new-born Children, fo as to fit the Fye for Vifion, which it is not, thro* the Deficiency and Muddinefs of the aqueous Humour, till fome time after Birth. This again may be confidered as a Cir- cumflance, that favours our prefent Conjeblures. As to the radiated Fibres of the Iris, and theCiliar Ligament, they do not feem fo much to be excited to Action by any external Influence, as to be kept in a State of conflant fmall Activity by the Vibrations which defeend from the Brain. When therefore the Rings are relaxed, the radiated Fibres will open the Pupil, and the Ciliar Ligament draw out the CapfuJa of the Cryflalline to a flatter Shape, and thus fuit the Eye to obfcure and diflant Obje&s. PROP. 63. *To explain the Manner and Degree, in which the automatic Motions, mentioned in the laji Proportion, are influenced by voluntary and Jem 1 voluntary Powers. CINCE the Motions of the Eyes are in every In- ^ ftance congruous, from the Inflant of Birth, an aflfociated Tendency thereto is generated fooner, and more firmly eftabliihed, than perhaps in any other Cafe. As therefore the external Influence of Light, by growing languid, comes to have lefs and lefsEffedt perpetually for this Purpofe, fo the aflbeiated Tendency grows ftronger and ftronger; and the Sum total of both may perhaps be always about equal. However, this Congruity does not feem to be fo great in Children as in Adults, who can direbt their Optic Axes by a perfectly voluntary Power to the Ob¬ ject which they intend to view with Attention. We muff examine therefore, how the almoft perfebt Con¬ gruity becomes an intirely perfebt one. Now