277] 



TIDAL FRICTION. 



501 



Since in these expressions n t + x/a + e measures the hour-angle 

 of the moon past the meridian of any point (x) on the canal, it 

 appears that high-water will follow the moon s transit at an in 

 terval ^ given by n t-^ = %. 



If c 2 &amp;lt; w 2 a 2 , or h/a &amp;lt; n 2 a/g, we should in the case of infinitesimal 

 friction have ^ = 90, i.e. the tides would be inverted (cf. Art. 178). 

 With sensible friction, ^ will lie between 90 and 45, and the 

 time of high-water is accelerated by the time-equivalent of the 

 angle 90 %. 



On the other hand, when hi a &amp;gt; n 2 a/g, so that in the absence of 

 friction the tides would be direct, the value of ^ lies between 

 and 45, and the time of high-water is retarded by the time- 

 equivalent of this angle. 



The figures shew the two cases. The letters J/, M indicate the positions 

 of the moon and anti-moon (see p. 365) supposed situate in the plane of the 

 equator, and the curved arrows shew the direction of the earth s rotation. 



It is evident that in each case the attraction of the disturbing 



