VOL. XIV .] PHILOSOPHICAL TRANSACTIONS. 43 



runs strongest. The arches are very wide, and have their feet secured by 2 

 pedestals that encompass them. Both these pedestals have their several degrees 

 or ranks of juttings out, like so many rows of stairs, the lowermost order pro- 

 jecting out most, the others being less, and going gradually more in ; the second 

 or uppermost pedestal is much less than the first or lowermost, being built a 

 little within its lines of circumference. Between the great arches there are win- 

 dows, or, as it were, small arches, that come down to the very plane of the 

 second, or uppermost pedestal, dividing the feet of the great arches. From 

 this rude description it appears that the Romans have here contrived every means 

 to break gradually the mighty force of the Rhone, and to render its passage easy 

 and inoffensive to the feet of the great arches; for here we see as many several 

 palisadoes and sluices as may be sufficient to defend this wonderful fabric against 

 all attacks of the torrent. The several ranks of stairs jutting from the pedestals, 

 which are for the most part triangularly built, and well faced with free-stone, 

 oppose and break the stream severally, or after each other, by reason of their 

 various inequalities in jutting out, in case the flood should swell so high, as it 

 frequently does, as to cover both the pedestals, then the small arches dividing 

 the feet of the great ones help to convey the water through, which otherwise 

 might endanger the great arches. 



Dr. Lister adds the following remark, viz. What seems to be the foot of the 

 arch is a horizontal arch gradually contracted, every stone being of vast length 

 and wedge-like, laid level with the water. 



Abstract of a Letter from Mr. A. Leuwenhoeck of Delft, concerning Scales 

 within the Mouth, the Scaly Child that was shown, the Anatomy of the Slime 

 within the Guts, and the Use of it. N° l6o, p. 586. 



In a former letter, I said that our skin was covered with scales, I have since 

 that time examined the cuticula of the inside of the mouth, and chiefly that 

 of the under lip, which I find to be covered with scales, larger than those on 

 the body, but thinner. As the scales of our body lying over each other, so as 

 to be 3 deep, are the cause of the skin appearing white; for diaphanous par- 

 ticles laid upon each other, and not too close, make a white; for which reason 

 we see that paper, spittle, beaten glass, and snow, are white ; so the scales of 

 our mouth lying but a little over the sides of each other, suffer the redness of 

 the flesh and blood to appear through them, and for this cause the lips and 

 mouth are red. 



1 have often wondered what should be the cause that a single hair lying on 

 the skin caused so great a tickling. But if the skin be covered with scales, and 

 the outward bark of the hair very rugged, it will not be strange that a hair lying 



G 2 



