Sacred philosophy of the seasons : illustrating the perfections of God in the phenomena of the year ... Summer / [Henry Duncan].

  • Duncan, Henry, 1774-1846
Date:
1837
Catalogue details

Licence: Public Domain Mark

Credit: Sacred philosophy of the seasons : illustrating the perfections of God in the phenomena of the year ... Summer / [Henry Duncan]. Source: Wellcome Collection.

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    dify and combine them in a certain order, and to convey them in regular succession, and without confusion, to the immediate seat of sensation. Yet this process, complicated as it may appear, consti- tutes but the first stage of the entire function of percep- tion; for, before the mind can arrive at a distinct know- ledge of the presence and peculiar qualities of the ex- ternal object which gives rise to the sensation, a long series of mental changes must intervene, and many intel- lectual operations must be performed. All these take place in such rapid succession, that, even when we in- clude the movement of the limb, which is consequent on the perception, and which we naturally consider as part of the same action, the whole appears to occupy but a single instant. Upon a careful analysis of the pheno- menon, however, it has been found that no less than twelve distinguishable kinds of changes must always in- tervene, in regular succession, between the action of the external object on the organ of sense, and the voluntary movement of the limb which it excites. The external agents capable of affecting the different parts of the nervous system, so as to produce sensation, are of different kinds, and are governed by laws peculiar to themselves. The structure of the organ is accordingly adapted, in each particular case, to receive the impres- sions made by such agents, and is modified in exact con- formity to the laws they obey. Thus the retina is adapt- ed to the action of light, and the various parts of the eye through which the rays pass, before reaching the retina, are constructed with strict regard to the laws of optics. In like manner, the ear is so formed as to receive deli- cate impressions from those vibrations of the air which occasion sound. The function of each nerve of sense is determinate, and can be executed by no other part of the nervous system. The functions are not interchange- able, as is the case with many others in animal life. No nerve but the optic nerve, and no part of that nerve ex- cept the retina, is capable, however impressed, of giving