264 MR. A. K. HTTNT OlS" THE INFLTTE]S"CB OF 



current would be rapidly shifting, so that a bottle would be con- 

 tinually moving about if the water were able to move it at all . I 

 think therefore that, even with a depth as great as 40 fathoms, 

 the effect of the waves is not to be disregarded, at least in the case 

 of a locality subject to oceanic swells, and where there is a sen- 

 sible tidal current as well. It is likely enough that it is only in 

 the case of a specially heavy ground swell that the effect of the 

 waves would be liable to be significant. ... I need hardly 

 say that if the depth be less than what I have supposed, the pro- 

 portion of wave-velocity to that at the surface for a given period 

 of wave will be greater than the eight fifteenths I have calculated 

 for the case chosen, and that same proportion of eight fifteenths 

 would be attained for waves of a smaller period than 17 seconds." 



As Professor Stokes has referred to wave-currents of 1 mile per 

 hour as being possible at a depth of 40 fathoms, it may be as well 

 to state what effect such currents would be capable of producing, 

 without taking into account the increase in power due to their 

 reciprocal character. 



According to Minard, quoted by Mr. T. Stevenson (' On Har- 

 bours,' p. 238), a current of 0"6819 mile per hour will sweep 

 along fine gravel, and a current o£ 1*3638 mile an hour will roll 

 along rounded pebbles 1 inch in diameter. Thus the 1-mile cur- 

 rent is more than sufBcient to roll along fine gravel. 



There is thus no lack of evidence that the power of wave-cur- 

 rents at a depth of 40 fathoms is occasionally considerable ; that 

 it is by no means exhausted at that depth ; and that, for the occa- 

 sional disturbance of a sandy bottom, the depth of 50 fathoms 

 may be attained, or even exceeded. 



The extreme limit of depth affected by wave-currents is of minor 

 importance in the present inquiry ; it will suffice if it be conceded 

 that appreciable wave-disturbance is occasionally experienced on 

 the sea-bottom at the depth of 50 fathoms. 



The occasional existence of such alternating currents being 

 granted — and of their presence between tide-marks and in shallow 

 water any observer can have ocular demonstration — we proceed 

 to inquire whether the fauna inhabiting shallow and exposed seas 

 is to an appreciable extent influenced by them. From the limited 

 observations I have been able to make, I am disposed to think 

 that the marine fauna referred to is influenced by such wave- 

 currents to an extent that it is scarcely possible to overrate. 



