2 British Association for the Advaficement of Science. 



a heavy body would acquire in falling through half the depth of 

 the fluid, so that 



In a channel about 4 inches deep, the velocity of the wave 



is nearly 2 miles an hour. 



It also appears that the breadth of the channel, when the depth 

 is given, does not at all affect the velocity or form of the wave ; 

 and Mr. Russell then proceeded to assign a general rule, by means 

 of which the velocity of the wave might be assigned a priori for 

 a channel of any form, however irregular. 



The manner in which the wave was observed, was by succes- 

 sive reflections from opposite surfaces, so as to make it pass and 

 repass a given station of observation, the interval being noted by 

 an accurate chronometer ; and it was stated, that in many cases, 

 above sixty transits of the same wave had been observed, so as to 

 give a high degree of accuracy to the observations. The instant 

 of the wave's transit had been observed by the reflection of a lu- 

 minous image, thrown down by a series of mirrors, so as to cross 

 micrometer wires with perfect precision. For a mode of deter- 

 mining the length of the wave, Mr. Russell acknowledged him- 

 self indebted to Prof Stevelly, of Belfast. 



These observations, having determined the laws of the propa- 

 gation of waves on a small experimental scale, were then extended 

 to the analogous phenomena of the great tidal wave. In his 

 observations on the River Dee, Mr. Russell found that the tide 

 wave followed precisely the same laws as those in his experimen- 

 tal channel ; that its velocity vj^as exactly proportioned to the 

 square root of the depth of the fluid, that its form changed in the 

 same manner, and the existence of the same law was suflicient to 

 account for the different rate of propagation of different tides be- 

 tween two given places, because a tide of fifteen feet deep would 



