Mr. A. Tylor on Tides and Waves. 209 



In fig. 4, PL IV., I take a particle of water at certain points on 

 opposite hemispheres, and show the direction of the resultants 

 of the two forces (the moon and earth's attraction) and the pro- 

 bable deflection of the moon's attractive rays in passing through 

 the earth. Sir J. Herschel (p. 528) only gives one position on 

 his Plate (p. 464), and leaves it to the reader to try the position 

 of particles on other parts of the circle and find their direction. 

 I have tried to do so according to his rule, and find that his 

 diagram would only apply to the moon's attraction by the earth 

 at such an immense distance that gravity could be considered as 

 acting to and from single points, viz. the centres of the two 

 attracting bodies, and surface attractions need not be considered. 

 Now the case of the tides is clearly that of a point or particle 

 at the surface of the earth being attracted by the two centres of 

 the earth and moon. HerschePs figure (p. 464) is not appropri* 

 ate to the conditions of the tides ; for it has no special relation 

 to surface attraction at all. If it proved any thing about tides, 

 it would prove there would only be a tide every twenty-four 

 hours. On the contrary, in fig. 4, PI. IV., I take into account 

 the deflection of the rays of attraction on entering the earth, 

 and find that, if they pass through the earth with the rapidity 

 of light, when they reach the other hemisphere they cause a 

 twelve-hours tide, simultaneously produced to that on the oppo- 

 site side of the globe. 



I have proved by analyzing the experiments on waves 

 by J. S. Russell and by Darcy, that the velocity measured in 

 feet per second of any wave when generated does not exceed 

 three times the cube root of the depth of the water it was gene- 

 rated in, measured in feet; that is, v=S^/p, a new formula, 

 which answers both for small and great depths, the usual for- 

 mulae giving results much too high for waves generated in deep 

 water. 



Mr. W. Parkes (Phil. Trans. 1868) suggests that the al- 

 ternate tides are produced in different hemispheres, and that 

 the evening tide which reaches Kurrachee twelve hours after 

 the morning has travelled a greater distance. This does not 

 seem probable; nor does he give any evidence on the point. 

 Then, with regard to the diurnal variations of the two tides, 

 Mr. W. Parkes (p. 686y says the diurnal inequalities disappear 

 when the attracting bodies are in the plane of the equator. It 

 appears to me, from the observations at Kurrachee, that when 

 the diurnal irregularity of the high-water points is at its 

 maximum, the diurnal irregularity of the low-water points is 

 at its minimum, and vice versa. Curiously enough, at Kurra- 

 chee the mean diurnal low-water irregularity is about 2 feet, 

 against about 1 foot (the mean diurnal irregularity of the high 



Phil. Mag. S. 4. Vol. 48. No. 317. Sept. 1874. ' P 



