R I V 



Explanation of the Table of Refractiont. 



The apparent altitude being found in the first column, the second shor/s 

 the refraction when the barometer stands at 30 inches, which is its mean 

 height oil the level of the sea, and the thermometer at 50 of Fahrenheit. 

 The third column contains the difference to be subtracted or added for 

 every minute of altitude, reckoned from the nearest number in the first 

 column. The fourth shows the number of seconds to be added for every 

 inch that the height of the barometer exceeds 30, or to be subtracted for 

 each inch that it wants of SO ; and the last contains the number of se- 

 conds to be subtracted for each degree that the thermometer stands above 

 50, or to be added for each degree that its height wants of 50. 



JEjr. At 7. 18'. 13". Bar. 29.87. Ther. 6Go. required refraction. 

 Alt. 7. 20'. R. 7'. 8" Diff. Alt. ",9 B. 14", 3 Th. ",63 



4- 1.62 K 47" =: 1'. 8 .13 1C 



4. 1,62 1,86 14,88 



1,86 



Ref. = 6. 52,83 



REFRANGIBIL1TY of lightSee Light. 



RESISTANCE of air to Projectiles. See Gunnery. 



RESISTANCE of Fluids. See Fluid*. 



RIVER. ( Du Buat, Rolison.) 



1. Let V = velocity of the stream por second in inches, R the quotient 

 arising from the division of the section of the stream, expressed in 

 square inches, by its perimeter minu the superficial breadth of the 

 stream in linear inches, S the slope the numerator being- unity, i.e. the 

 quotient arising from dividing the length of the stream, supposing it ex- 

 tended in a straight line, by the difference of level of its two extremities, 

 or l^t it be the cotangent of the inclination or slope ; then the section 

 and velocity being both supposed uniform, 



v = 



V, S I h. 1. /S -{ 



-__ -- 5, _ 



10 V, Si I h. 1. /S -{- i|\ 10 



When R and S are very great 



V=S E*(_2 -- *) nearly. 

 V si - \ h. L 9 ^ 



The elope remaining the mine, the velocities are a* v' R~ TT; or M 



R", when R u ver 

 216 



