338 Mr. R. Potter, Jun., on the Velocity with which 



Angle £*'y, fig. 1. = 5° 0' 6" 

 ef — = -0337193 

 ii fig. 2. = -1125248 

 er — = 12-10 

 r^ — = 20-04 

 This value of £ i being taken without removing the glasses, 

 on account of the great labour required to re-adjust the appa- 

 ratus, requires to be considered as for the distance rp cor- 

 rected by a a, fig. 2, which I calculated in the experiments 

 taken at and after this date from the expression : 



a a t = thickness of glass x / - ) 



whence ab = -1859400 and for p = 1/495 

 d-d, ._ •00037980- 



— J. OOc$» 



D y -D -0002446*4 

 On the same day, I obtained the following also : 

 Angle 5*y, fig. 1. = 9° 59' 42" 

 ef — = -1240136 

 It fig. 2. = -11339 

 er — = 12-10 

 rp — = 20-04 

 whence ab = -1873696, and when ft = 1-495 



d—d t _ -001419883 _ 

 D-D ~ -00092721 

 On the 8th of May, I obtained as follows : 



Angle ?iy, fig. 1. = 5° 0' 6". 



ef — = -047953687 

 ii fig. 2. = -0776168 

 er — = 12-05 

 rp — = 20*28 

 whence ab m -1303349, and takings = 1-405^ 

 d-d, -00037257 

 D y -D " -00023757 ~ 

 On May 9th, I obtained the following : 

 Angle ?*y, fig. 1. = 5° 0' 6" 



ef — = -04641225 

 fi fig. 2. = -0803153 

 er — = -12-05 

 rp — - = -20-26 

 whence a b = -1347321, and taking here /x = 1*492 

 d-d , - 00037475 

 D-D "" -00023915 " l ' 5b1 ' 



