Rev. 0. Fisher — "The Origin of Mountains" : a Reply. 435 



be unaffected by it." To this Colonel Burrard replies : " Mr. Fisher 

 has argued that the rotation of the earth will give to the liquid 

 interior an effective rigidity ; but this rotation has conferred no 

 rigidity upon our oceans, and even if it did render the liquid interior 

 rigid, it would only do so in low latitudes where the rotation 

 velocity is high. I understand, moreover, that the earth's interior 

 was assumed by Mr. Eisher to be liquid, in order to explain the 

 floatation of the crust. If the liquid is now proved to be rigid, 

 the crust cannot be floating upon it." Colonel Burrard forgets that the 

 ocean and the earth's crust, being part of the rotating mass, the forces 

 acting on them are internal, and will not be affected by the gyroscopic 

 rigidity, which exists only with reference to external forces. It is 

 true that this rigidity will be greatest in the equatorial regions, but 

 it is in those regions that the tidal forces chiefly act, and require to 

 be, and are, met by this theory. 



Colonel Burrard asks, "How can computers test a theory when 

 the limits and size of the roots are not exactly defined?" My 

 answer is, how can I define the limits and size of the roots, believing 

 as I do that mountains are partly supported by the rigidity of the 

 crust ? Is it likely that where the crust has been thickened by 

 compression, part being sheared upwards and part downwards into 

 the substratum, the compressed area should have become detached 

 from the adjoining crust, so as not to depress it to some distance 

 away, along with it? And if that depression became covered by 

 detritus it also would appear to have a root. In fact, the simplicity, 

 very naturally desired by geodesists, is not to be expected. But the 

 lack of it does not condemn the theory of mountains having roots 

 projecting into a dense liquid substratum, and that this arrangement 

 tends to produce isostasy. 



In a note at p. 387 Colonel Burrard controverts my argument 

 against solidity, drawn from the observed changes of gravity since 

 1873 at Dehra Dun ; and says that the change is apparent only and 

 due to the vibration of the pendulum's support. But in his paper at 

 the Royal Society, 1906, he wrote: "The only faults which have been 

 found with their [the observers' of 1865-73] work, are such as would 

 tend to produce constant error." And he gives the following list: — 



Now it will be seen that the difference at the four stations mentioned 

 is not constant, but is more than twice as great at Dehra Dun than 

 at the other three. This would be in accordance with the changes 

 still said to be going on there, to which I referred as reported in 

 Nature. 



