84 PRODUCTION SECT. XIV. 2. 3. 



us ; and have finally allowed, that all our knowledge is derived 

 through the medium of our fenfes ! They forget, that if the 

 fpirit of animation had no properties in common with mfltter, it 

 could neither affect nor be affected by the material body. But 

 the knowledge of our own material exiftence being granted, 

 which I fufpecl few rational perfons will ferioufly deny, the ex- 

 igence of a material external world follows in courfe ; as our 

 perceptions, when we are awake and not infane, are diftingufh- 

 ed from thofe excited by fenfation, as in our dreams, and from 

 thofe excited by volition or by afTociation, as in infanity and 

 reverie, by the power we have of comparing the prefent percep- 

 tions of one fenfe with thofe of another, as explained in Seel:. 

 XIV. 2. 5. And alfo by comparing the tribes of ideas, which 

 the lymbols of pictures, or of languages, fuggeft to us by intui- 

 tive analogy with our previous experience, that is, with the com- 

 mon courfe of nature. See Clafs III. 2. 2. 3. on Credulity. 



3. Of the Penetrability of Matter. 



The impoflibility of two bodies exifting together in the fame 

 fpace cannot be deduced from our idea of folidity, or of figure. 

 As foon as we perceive the motions of objects that furround us, 

 and learn that we pofTefs a power to move our own bodies, we 

 experience, that thofe objects, which excite in us the idea of 

 folidity and of figure, oppofe this voluntary movement of our 

 own organs ; as whilft I endeavour to comprefs between my 

 hands an ivory ball into a fpheroid. And we are hence taught 

 by experience, that our own body and thofe, which we touch, 

 cannot exift in the fame part of fpace. 



But this by no means demonftrates, that no two bodies can 

 exift together in the fame part of fpace. Galilseo in the preface 

 t'i his works feemVto be of opinion, that matter is not impene- 

 trable : Mr Mitchel, and Mr. Bofcowich,in his Theoria Philof. 

 Natur. have efpoufed this hypothefis : which has been lately 

 publifhed by Dr. Prieftley, to whom the world is much indebted 

 for fo many important difcoveries in fcience. (Hift. of Light 

 and Colours, p. 391.) The uninterrupted paflage of light 

 through tranfparent bodies, of the electric sether through metal- 

 lic and aqueous bodies, and of the magnetic effluvia through all 

 bodies, would feem to give fome probability to this opinion. 

 Hence it appears, that beings may exift without poflefiing the 

 property of folidity, as well as they can exift without pofTefiing 

 the properties, which excite our fmell or tafte, and can thence 

 occupy fpace without detruding other bodies from it ; but we 

 cannot become acquainted with fuch beings by our fenfe of 



touch, 



