DESCRIPTION OF A RHEUMAMETER. ^J 



Second siluatioiif in the middle of the stream. 



1 HO 



2 14 S .6tD9: 21to3lJ 



^ 14 } 



Third situation, \5 yards from the side^ opposite the street 

 des Saints- Peres. 



1 28 ^ 



2 o8 > lto2: S^ to 7 



3 26 J 



Though these data are not very ample, it is obvious, GeneralcoTi« 



1st, That the water at the sides of rivers has but little. elusions, 

 velocity : and 



2dly, Xhat the velocity of the middle of the stream in- 

 creases in an extraordinary degree the impulsive force; 

 since the action produced on the log by a velocity of iO met. 

 [32f. 9 in.] in 14 seconds was from 21 ounces to 31|; while 

 by a velocity of 28 seconds it was only from 3j- oz. to 7« 



On comparing afterward our experiments with those ofTheexperi- 

 Mariotte, made about \6GG in the same place, we found a o„e"inUie^*''' 

 great deal of similarity in the results." By means of little I7ih century, 

 balls of wax, ballasted so as to swim level with the surface, 

 he estimated the velocity of the Seine, at its mean height, to 

 be 150 feet in a minute, or 30 inches in a second. But 

 when we made our experiments the Seine was only 4^ feet 

 high, and at the timeof Mariotte*s it was 5 feet; a differ- 

 ence in height answering to the difference of velocity. And 

 hence we may infer, that a century and half has made no 

 change in the current of the river at this part. 



The same experiments led us to compare the velocity of Velocity of the 

 the Danube with that of the Seine. In the Journal de Jt)anube. 

 Paris, of the 11th of July, 1809, is a note from Baron Pa- 

 kali, who says, that the velocity of the Danube, at its mean 

 height at Ebersdorf, is 4| feet in a second ; so that we may 

 consider it twice as rapid as the Seine at Paris. 



Erplanatim of the Plate, 

 PI. II, fig. 3. a, a cube of cork, 4 inches square, bound Explanatlontf 

 round with pjickthread to strenglhen it. ^^« P'*^«« 



