360 



REPORT — 1844. 



Table XVII. 



Observations on the Diffusion of the Wave of the First Order round an Axis 

 of origiiuil Transmission. 



The observations were made upon the wave at various points in circles of 

 9 and 15 feet radius, described from the outer extremity of the side of the 

 channel C, as shown in Plate LIV. fig. 3. The depth of the water when at 

 rest was taken at the various points, and these being subtracted from the 

 absolute heio-ht to which the wave attained in its transit, gave the amounts 

 which are contained in the lower part of the table, the absolute heights from 

 which these are deduced being given immediately above in columns marked 

 thus. A, B, C, D, E, while the deducted heights are distinguished thus, A', B', 

 C, D', E'. Experiments VII. to XV. were made in the 9 feet circle, and the 

 remainder in that of 15 feet radius. It will be observed that in the latter set 

 there are two columns which are headed zero, but it must be remembered 

 that the one in brackets contains observations which were made at the 9 feet 

 distance along the axis and the remainder on the outer circle. 



Fjg. 3 contains the approximate ratio of the height of the wave at different 

 points in the circumference of the circles expressed by lines concentric to the 

 circles, each of which denotes the tenth part of an inch. 



The observations are laid down accurately in the diagrams, where the 

 lines A B and C D represent the circumference of the quadrants of the ob- 

 served circles. Upon these lines the true heights of the wave are measured 

 upwards at their respective points of observation, and a curve drawn through 

 these, representing the mean of the wave's height. From these and from a 

 numerical discussion of the observations, it appears that the height of the 

 wave at 0'^ being 1, its height at the remaining points will be |, f , ^, and -^^, 

 or taking integral numbers to express the ratio, it will stand thus, 30, 15, 12, 

 10, 3. And from a discussion of the whole of the experiments it is found 

 that the height of the wave is inversely as the distance from the centre. 



Fig. 4 shows the appearance of the wave upon which these observations 

 were made. 



