SUMMARY OF HYDRAULICS. $7 



Water has been fometimes raifed by fluffed cufhlons con-Cellular pumps 

 Jieded with an endlefs rope,, and caufed by means of two J^" 110 *" 

 wheels or drums to rife in fucceffion in the fame barrel, and to 

 carry water with them : but the magnitude of the friction ap- The chain- 

 pears to be an objection. From the refemblance of the appa-P um P* 

 ra( us to a firing of beads, it has be^n called a paternofter work. 

 When flat boards are united by chains,. and employed inftead of 

 thefe cufhions, the machine may, without impropriety, be called 

 a cellular pump : here the barrel is generally fquare, and placed 

 in an inclined pofition. But thefe machines are very rarely 

 employed. 



Chapter 24. Of inftruments for meafuring the velocity of 

 ftreams of water. 



The fuperficial velocity of a ftream is afcertained without Inftruments for 

 difficulty, by obferving in calm weather the motion of a body ^loctty^ 

 barely floating on it. But it is more difficult to determine the ftreams of water, 

 velocity of a river at a confiderable depth. Pitot's tube, as im- 

 proved by Buat, furnifhes one of the eafieft methods. A funnel 

 is prefented to the ftream, and the water in a vertical tube con- 

 nected with it, is elevated above the level of the river, nearly 

 to the height correfponding to the velocity : but the refult will 

 be more accurate, if the funnel be covered by a plate perforated 

 only in the centre by a fmall orifice : in this cafe, the elevation 

 in the tube will be half as great again as the height due to the 

 velocity. Other inftruments for appreciating the impulfe of 

 the water againft. a flat board, require fome previous compara- 

 tive obfervation. In Woltmann's hydrometrical fly, the num- 

 ber of revolutions of a wheel, in a given time, indicates the ve- 

 locity of the water, which ftrikes againft two inclined planes, 

 and carries round the arm to which they are fixed. 



It is prefumed, that this abridged account of Mr. Eytel- Concluding ad- 

 wein's book, will not only do juftice to his diligence and inge- 

 nuity, but will convey to the Englifli reader fome matter per- 

 fectly new, and capable of frequent application in practical 

 hydraulics ; which is perhaps of the more value, as there is 

 little probability that the work will be tranflated at length. To 

 diifeminate information of this kind muft always be the prin- .. .. 



cipal objeft of the Journals of the Royal Inftitution. 



Y. 



IV. Experiments 



