Correspondence — Mr. A. R. Hunt. 527 



scientific papers where the metrical system is used, it is to be 

 inferred that they are capable of learning that system, which is 

 not more difficult than the multiplication table of 10. 



The prognostications of your correspondent I fear are of little 

 value, for I find daily the metrical system is replacing more and 

 more the barbai'ous standards. I know of some large English 

 engineering works recently opened in Italy where all the English 

 engineers, after a few months' absence from home, adopt the metrical 

 system as far as the inch-calihred machinery will allow, and con- 

 stantly grumble at the two-foot rule. 



Lastly, allow me to state that once it was my practice to put old 

 English equivalents by the side of the metrical measurements, but 

 I dropped the practice because one Editor wrote to me saying that 

 it was a presupposed fact that the readers of his journal understood 

 the metrical system, and it might offend their dignity to be told the 

 English equivalent of 2-5 centimetres, etc. Another Editor wrote 

 that it was superfluous and added to the length of the paper. 



Chemists and physicists have universally adopted the metrical 

 system, mathematicians, astronomers, etc., prefer it, and I maintain 

 that geologists — especially those who write for the future in the 

 Geol. Mag. — the least conservative of all scientists, should not be 

 the last to give up an archaic if not an archean system. 



Naples, Oct. Uth, 1890. H. J. Johnston-Lavis. 



WIND WAVES AND TIDAL CURRENTS. 



Sir, — Allow me to thank Mr. Stirrup for the invaluable informa- 

 tion contained in his letter on " Wind Waves and Tidal Currents." 

 It does not, however, affect the position taken up in my letter on 

 "Tidal Action " as to the question of the action or inaction of Tidal 

 currents on the floor of the English Channel. The Mediterranean 

 being practical^ a tideless sea, the currents encountered by M. Fol 

 could not possibly be Tidal, and herein lies the extreme value of 

 the observations. 



My investigation of wave-action was undertaken in order to prove 

 the disturbing power of waves on the sea-bottom, and I proved my 

 point up to the hilt, and indeed a little further, as the ascertained 

 amount of disturbance exceeded what the theory of oscillating waves 

 would allow. 



In a paper submitted to the British Association in 1886, I pointed 

 to the clean sand and shells in 100 fathoms and more at the mouth 

 of the English Channel as evidence of the presence of wave-currents 

 at a depth far below the reach of the heaviest oscillating waves, and 

 said that " the presence of this deposit of clean sand and shells is 

 at present unaccounted for, for there are no recognized agents 

 competent to disturb and distribute such material below the depth of 

 fifty fathoms:" at the same time I showed how a gale off Queens- 

 town by the general disturbance of the water-level, stirred up sea- 

 weed in Torquay Harbour far beyond the radius of the atmospheric 

 disturbance caused by the storm. 



In a tidal sea it is impossible to isolate these far-reaching currents 



