324 



The "<age of the tide," or the mean interval from full and change of moon to springs, is (197° -8 - 172" • 3) 

 -=-l°'016 hours, or 25 hours. This is a normal result, for the ages at Madras, Bombay, and Karachi are 

 29 hours, 32 hours, and 27| hours, respectively. 



The diurnal tides are well marked, as might be expected : and it is interesting to note that they 

 are "direct" and almost exactly in the phase indicated by the equili))rium theory. The age of the 

 diurnal inecjuality may be defined as the mean interval which occurs after the moon has attained her 

 maximum declination before the diurnal tide reaches its maximum. This is given by the excess of k- 

 for Ki over k for O, divided by twice the moon's mean motion. Thus, in the present case, the age is 

 {14:°'6 - ( - 1''0)} -^ l°-098 hours, or 14-| hours. There does not seem to be any prevalent rule as to 

 this "age" in India, for whereas at Madi'as the corresponding period is 14 houi's, at Bombay and Karachi 

 this retardation is replaced by a small acceleration. 



These results are very valuable, as relating to the only ocean uninterrupted l(y land throughout the 

 whole circumference of the glolie, yet in themselves they do not seem to present any features of special 

 interest. But they do acquire much importance when considered in connection with the very abnormal 

 results obtained by the " Discovery," which I hope to discuss in the volumes to be devoted to the 

 scientific work of that expedition. 



I wish to use the present opportunity of drav.-ing attention to a mistake which was made in the article 

 on Tides in the ' Admiralty Scientific Mainial.' It was discovered Ijy Mr. Selby when he came to apply 

 the methods of that article to these reductions. The mistake occurs in the ' British Association Report ' 

 for 1886, referred to above by Mr. Selby, and was carried on into the Manual. The principle of the 

 method was given correctly in my paper in the ' Proceedings of the Royal Society ' for 1893, vol. 52, p. 365, 

 l:)ut certain small changes are needed for applying the method to the case in point. 



I hope to correct the mistake in vol. 1 of my Collected Papers, which are to lie published by the 

 Cambridge University Press, l)ut it may sufHce here merely to correct the errata in the Manual as 

 follows : — 



At p. 63, — Fm' the tuJes Ko niul S. In the fornmla for tan if, in the denominator, for 3-67 p, read 

 3 '71 p, for a fortnight's observation, and 3-84 p, for a month's observation. In the formula for H^, 

 wherever 3 '67 occurs, read 3 '71 for a fortnight, and 3-84 for a month's observation. The formula 



H" = r H. remains correct. 



3-67 



For the lid/'s Ki and P. In the formula for H' the 3 in the numerator (lint not that in the denominator) 

 should be replaced by 3 -007 for a fortnight's observation, or by 3 '027 for a month's observation. The 

 formula Hp = iH' remains correct. 



For k' = Kp = C + V' + </j read 



K = Kp = f' + V' + <^ + 6°-88 for a fortnight, and k' = Kp = {■' + V' + <^+ 13°-29 for a month. 



The succeeding numerical example must be corrected accordingly. The only sensible change is that 

 K = Kp = 334° in place of 327°. 



G. H. Darwin. 



December, 1906. 



