In the _Sixth_, After he hath shew'd, what is to be understood by what we call _Soul_, and by what we call _Body_, he labours to make it out, that we are much more assured of the Existence of the Soul, than of that of the Body, which he conceives he can prove from hence, that we cannot doubt, that we think, because even doubting is thinking; but one may doubt, whether one has a body, for several reasons, which he alledges, and thinks so cogent, that he concludes, it is not evident to him by the light of reason, that he has a Body. But supposing, there be Bodies, he examines, what are the Operations, that belong to the Soul, and what those, that belong to the Body; and lastly, what those, that result from the Union of both: And then explains, how all those operations are perform'd, and particularly, _Sensation_; where he shews, that the Nerves, holding at one end to the Brain, whereof they are but Allongations, and being at the other end extended to the extremities of the Body; when an Object comes to touch those exterior ends of the Nerves, the interior ones in the Brain are presently shaken; and cause different sensations according to the diversitie of Nerves, and the differing manner, in which they are shaken. And to shew, that 'tis this shaking, that causes Sensation, he notes, that if any thing shakes the interior parts of the Nerves, though the object be absent, the Soul has presently the same {310} sensations, as it would have, if it were present. As, if one should knock on's head forcibly against a wall, the shaking, which the blow gives to the Brain, moving the interior extremities of the Nerve, which causes the sensation of Light, the Soul has the same sensation, which it would have, if it saw a thousand Candles: On the contrary, if the interior extremities of the nerves are not shaken, though the object be present, it causes no sensation; whence it comes, that if a strong Ligature be made upon the middle of the Arm, and the hand be then prickt, no pain is felt, because the shaking of the nerves that are pricked, being stopped by the Ligature, cannot reach to the extremities of the Nerves, that are within the Brain. * * * * * _Advertisement._ The following _Errata_, left by the _Press_ in _Num._ 16, the _Reader_ is desired thus to correct. Page 269. lin 27. read, _motion of B above the Center; G. is also_, with a _Semi-colon_ after the word _Center_. p. 274. l. 13, r. _it to do to the_. p. 277. l. 24. r. _natural days_. p. 281. l. 16. r. _of his_. ib. l. 27. r. _a notion_. p. 293. l. 4. r. _enough without_. ib. l. 43. r. _to the Sine of_. p. 294. l. 1. r. _to the Sine of_. * * * * * _LONDON_, Printed for _John Martin_ and _James Alestry_, Printers to the Royal Society. 1666. {311} * * * * * _Numb._ 18. PHILOSOPHICAL _TRANSACTIONS._ * * * * * _Munday_, _October_ 22. 1666.