Proceedings of the British Association. 557 



Feet per second. Feet. 



3.37 3.26 



3.57 3.57 



3.72 3.913 



3.84 4.20 



4.16 5.00 



4.62 6.25 



He had also completed some further examinations of the wave of 

 the first order, and could now present the subject in a tolerable 

 complete form. 



Prof. Braschmann inquired whether he was to understand Mr. Russell 

 as saying, that the very beautiful method described by him, of finding the 

 velocity of a stream, gave merely the velocity of the surface, or the 

 mean velocity of the section. — Mr. Russell replied, merely the velo- 

 city of the surface. — Prof. Braschmann said, that in that case it could 

 not be made available in the present state of our knowledge for enabling 

 us to determine the mean velocity, which was what, in practice, we 

 required, as no known relation existed between it and superficial 

 velocity ; depending as it did for its value on the configuration of 

 the canal, and form and magnitude of the section. There existed no 

 branch of hydraulics in a more imperfect and unsatisfactory state 

 than this ; all the approximations at present used being very rude 

 and uncertain in their application. Prof. Whewell inquired whether Mr. 

 Russell found the depth to which the disturbing wire was inserted 

 into the fluid to be of any consequence. — Mr. Russell replied, not 

 the slightest ; the merest contact of the wire to the fluid produced 

 precisely the same phenomena as its deepest insertion. — Prof. Whewell 

 inquired how the hinder part of the curve, which these capillary waves 

 formed at slow velocities, disappeared as the velocities increased. — Mr. 

 Russell replied, that the hinder part of the curve drew up to the exciting 

 wire, and at length, as the lateral branches extended, it appeared as 

 if obliterated. — Dr. Scoresby inquired whether, as the number of waves 

 increased with the increase of velocity, those which were most remote 

 from the exciting wire did not diminish in height ; and if so, whether 

 they did not also increase in breadth or distance between summit 

 and summit. — Mr. Russell replied, that to this point he had paid 

 the earliest and most minute attention, so that he was able to assert, 

 with the utmost confidence, that although the waves more distant from 

 the exciting wire diminished in height, yet the wave length, or distance 

 from summit to summit, was everywhere, at the same velocity, equal ; 

 so that in equal spaces, taken at whatever distance from the wire, 



