we conceive. Something perfectly analogous to this may be remarked in the perceptions we obtain by the fense of fight. When I look into a fhew-box, where the deception is imperfect, I fee only a set of paltry dawbings of a few inches diameter; but, if the reprefentation be executed with so much skill, as to convey to me the idea of a diftant profpect, every object before me fwells in its dimenfions, in pròportion to the extent of fpace which I conceive it to occupy; and what feemed before to be fhut up within the limits of a small wooden frame, is magnified, in my apprehenfion, to an immenfe landscape of woods, rivers, and mountains.

The phenomena which we have hitherto explained, take place when fleep feems to be complete; that is, when the mind lofes its influence over all those powers whose exercise depends on its will. There are, however, many cases in which fleep seems to be partial ; that is, when the mind lofes its influence over fome powers, and retains it over others. In the case of the fomnambuli, it retains its power over the limbs, but it poffeffes no influence over its own thoughts, and scarcely any over the body; excepting thofe particular members of it which are employed in walking. In madness, the power of the will over the body remains undiminished, while its influence in regulating the train of thought is in a great measure fufpended; either in confequence of a particular idea, which engroffes the attention, to the exclufion of every thing else, and which we find it impoffible to banish by our efforts; or in confequence of our thoughts fucceeding each other with fuch ra-pidity, that we are unable to stop the train. In both

of

of these kinds of madness, it is worthy of remark, that the conceptions or imaginations of the mind becoming independent of our will, they are apt to be mistaken for actual perceptions, and to affect us the fame in

manner.

By means of this fuppofition of a partial sleep, any apparent exceptions which the hiftory of dreams may afford to the general principles already ftated, admit of an eafy explanation.

Upon reviewing the foregoing obfervations, it does not occur to me, that I have in any inftance tranfgreffed those rules of philofophifing, which, fince the time of Newton, are commonly appealed to, as the tests of found inveftigation. For, in the first place, I have not supposed any causes which are not known to exift; and fecondly, I have fhewn, that the phenomena under our confideration are neceffary confequences of the causes to which I have referred them. I have not supposed, that the mind acquires in fleep, any new faculty of which we are not confcious while awake; but only (what we know to be a fact) that it retains fome of its powers, while the exercife of others is fufpended and I have deduced fynthetically, the known phenomena of dreaming, from the operation of a particular clafs of our faculties, uncorrected by the operation of another. I flatter myfelf, therefore, that this inquiry will not only throw fome light on the ftate of the mind in fleep; but that it will have a tendency to illuftrate the mutual adaptation and fubferviency which exifts among the different parts of our conftitution, when we are in complete poffeffion of all the faculties and principles which belong to our nature *.

*See Note [O].

CHAPTER FIFTH.

PART SECOND.

Of the influence of Affociation on the Intellectual and on the Active Powers.

SECTION I.

Of the Influence of cafual Associations on our speculative

THE

Conclufions.

HE Affociation of ideas has a tendency to warp our speculative opinions chiefly in the three fol lowing ways:

First, by blending together in our apprehenfions, things which are really distinct in their nature; so as to introduce perplexity and error into every process of reasoning in which they are involved.

Secondly, by misleading us in those anticipations of the future from the past, which our conftitution difpofes us to form, and which are the great

of our conduct in life.

foundation

Thirdly, by connecting in the mind erroneous opinions, with truths which irresistibly command our affent, and which we feel to be of importance to human happiness.

A fhort illustration of these remarks, will throw light on the origin of various prejudices; and may, perhaps, fuggeft

fuggest some practical hints with respect to the conduct of the understanding.

I.I formerly had occafion to mention feveral instances of very intimate affociations formed between two ideas which have no neceffary connexion with each other. One of the moft remarkable is, that which exists in every person's mind between the notions of colour and of extenfion. The former of these words expreffes (at least in the fenfe in which we commonly employ it) a fenfation in the mind; the latter denotes a quality of an external object; fo that there is, in fact, no more connexion between the two notions than between thofe of pain and of folidity*; and yet, in confequence of our always perceiving extenfion, at the fame time at which the fenfation of colour is excited in the mind, we find it impoffible to think of that sensation, without conceiving extenfion along with it.

Another intimate affociation is. formed in every mind between the ideas of space and of time. When we think of an interval of duration, we always conceive it as fomething analogous to a line, and we apply the fame language to both fubjects. We speak of a long and fhort time, as well as of a long and short distance; and we are not confcious of any metaphor in doing fo. Nay, fo very perfect does the analogy appear to us, that Bofcovich mentions it as a curious circumftance, that extenfion should have three dimenfions, and dura tion only one.

This apprehended analogy feems to be founded wholly on an affociation between the ideas of space and

See Note [P]).

of

of time, arifing from our always measuring the one of these quantities by the other. We measure time by motion, and motion by extenfion. In an hour, the hand of the clock moves over a certain space; in two hours, over double the space; and so on. Hence the ideas of space and of time become very intimately united, and we apply to the latter the words long and fhort, before and after, in the same manner as to the former.

The apprehended analogy between the relation which the different notes in the scale of mufic bear to each other, and the relation of fuperiority and inferiority, in respect of position, among material objects, arifes also from an accidental affociation of ideas.

What this affociation is founded upon, I fhall not take upon me to determine; but that it is the effect of accident, appears clearly from this, that it has not only been confined to particular ages and nations; but is the very reverse of an affociation which was once equally prevalent. It is obferved by Dr. Gregory, in the preface to his edition of Euclid's works, that the more ancient of the Greek writers looked upon grave founds as high, and acute ones as low; and that the prefent mode of expreffion on that fubject, was an innovation introduced at a later period *.

In the inftances which have now been mentioned, our habits of combining the notions of two things, becomes fo ftrong, that we find it impoffible to think of the one, without thinking at the fame time of the other. Various other examples of the fame fpecies