THE TIDAL WAVE ON THE OFF SIDE OF THE EARTH. 1 8'> 



The Lecturer here asked for a few minutes' indulgence, as his 

 voice was far from strong. His son, Dr. E. G. Hull, read some notes 

 on the same subject during the interval, and Colonel Yate having 

 been called away by his Parliamentary duties, Lieut. -Colonel G. 

 Mackinlay succeeded him in the Chair. 



The Lecturer then exhibited a number of slides illustrating the 

 form of the cotidal lines round the British Isles. 



Discussion. 



Colonel Mackinlay (as Chairman) said that he had not been quite 

 able to follow the first part of Professor Hull's lecture, and saw no 

 reason for giving up the usual explanation of the antipodal tide ; 

 namely, that the moon, acting upon the waters of the ocean, 

 attracted those on the nearer side somewhat more strongly than it 

 attracted the earth as a whole, so that the waters on that side were 

 heaped up towards the moon ; while its attraction on the waters on 

 the far side being less than on the earth, those waters were, in effect, 

 left behind. He found the second part of Professor Hull's lecture 

 very interesting, and especially his description of the troubled state 

 of the waters where the co-tidal waves round the British Isles meet 

 each other. 



Mr. Maunder said that the subject with which Professor Hull 

 had dealt was interesting to all. But he could not agree with the 

 Lecturer that there were many divergent theories as to the cause of 

 the tides. The Newtonian law of gravitation held good, and the 

 main cause of the tides was the attraction of the moon. But the 

 working out of the details of tidal movements was very complex, as 

 those who had seen Lord Kelvin's tide machine would quite 

 appreciate. The differences between various writers upon the 

 subject had been differences as to the method that should be 

 adopted in order to give the young student or general reader an 

 idea of the actual effect upon the waters of the moon's attraction 

 that should be at one and the same time readily intelligible and 

 sufficiently full and sound. 



Professor Hull, if he had correctly followed him, had taken up a 

 point which had sometimes been omitted from these popular 

 explanations. Eeferring to the diagram, Professor Hull had shown 

 that the action of the moon at the point E might be resolved into 

 two forces, EC 2 and C 2 M, of which EC' 2 was directed towards the 



