TKANSACTIONS OF THE SECTIONS. 



235 



V ■will be the velocity of the water in feet per second. 

 r/= accelerating force of gravity=32-18 feet per second. 

 w= weight of a cubic foot of water at dOP Fahr. 



jj = difference between the heights of the columns of water driven xva the tubes 

 measured in inches. 



"W= weight in lbs. of -^L cubic foot of water. 



The formula becomes •»= / 3^'18 



^= / 3-2-li 



r=V'^X 1-638. 



To' test the correctness of this by experiment, a steadily flowing stream was se- 

 lected. The speed taken by the motion of a body floating on it was found to be 1 foot 

 per second. The difference of the height of the water-columns was 0'375 inch. 

 According to the formula the speed would hare been 1-003 feet per second. This 

 close agreement between the results of experiment and of calculation proves the 

 correctness of the calculations, not only as regai'ds the rhysimeter, but as regards 

 the anemometer also. 



AVhen the speed of the water or other flowing liquid is so great as to make tho 

 difference between the heights of the columns in the indicator inconveniently long, 

 it is easy to introduce a siphon containing mercurj'. In this the motion will be 

 less in proportion as its specific gravity is greater than that of water. 



This is necessary when the rhysimeter is used to measm-e the speed of ships. 

 The formida then becomes p=v-x0-087'36, where d= velocity of the ship in knots 

 per hour, and ;; = height of column of mercury in inches. Below is a Table calcu- 

 lated from it ; its correctness has been abundantly proved by experience. 



Hydraulic-pressure tubes for measuring the speed of ships have been adopted by 

 Pitot, Darcy, Berthon, and Napier, but hitherto they have not been extensively 

 used by sea-going vessels. 



Table showing the Speed of a Ship as indicated by the Rhysimeter. 



;;=j;^-X 0-08736. 



Tablk showing the Speed of Cm-rents of Water as indicated by the Rhysimeter. 



r=v';^X 1-638. 



I 



