Mr. E. L. Garbett on Popular Difficulties in Tide Theory. 177 



and night breezes, in the very region where theory plainly 

 gives the attractions freest play ! Now, on reviewing the popular 

 expositions, I presently saw a flaw whose correction would just 

 tend, and is the only thing I can conceive tending, to explain this 

 general fact — the confinement of all extra large, and even of the 

 majority of decidedly sensible tides, to high, or at least extra- 

 tropical latitudes. 



In all theories the " solid " mass of the earth is regarded as 

 absolutely unyielding to the forces that deform its waters. This 

 involves attributing to it not merely solidity, but a wholly ima- 

 ginary strength or degree thereof, one of whose existence matter 

 nowhere gives us any trace of evidence. A glance at experiments 

 on the strongest materials, made for engineering data, shows 

 how small, compared with geographic distances, is the highest 

 precipice, for instance, that any known solid could form with- 

 out crushing its own base : — for ice, it is said, but 710 feet 6 ; 

 chalk and freestone little more than the highest of our cliffs of 

 them ; and no stone or metal probably over one mile. In the 

 experiments of M. Tresca, cold metals flow perfectly under pres- 

 sures less than exist at the first league or two underground 7 ; so 

 that a few miles below us an unfilled cavity could no more sus- 

 tain itself in cold iron or cold granite than in water. Now, is a 

 body transmitting -pressure in all directions, or wherein no cavity 

 can exist, to be called a solid or fluid ? In short, what definition 

 of a " solid " can we give apart from scale ? 8 Is not cold butter 

 or cold asphalt a solid on the scale of inch cubes, and a liquid 

 on the scale of the " pitch lake" in Trinidad ? Viewed on a ter- 

 restrial scale, what is the practical difference between the "soli- 

 dity " of calvesfoot jelly, whereof a precipice 3 feet high might 

 stand, and that of granite, wherein one of three miles might per- 

 haps be possible ? It is a question, you see, of the depth of 

 " superficial viscosity/ 3 as Van de Mensbrugghe and Mr. Tomlin- 

 son would say. The " solid " globe that all tide theories assume, 

 then, is seen to require some form of matter bearing to quartz 

 or diamond the relation that these bear to water; in short, 

 we are assuming what inductive reasoning has no right to, 

 something supernatural, i. e. a quality exalted to a degree not 

 approached in known nature. With her solids, or the utmost 

 solidity known of, we can get no globe whose behaviour to the 

 tidal forces will differ otherwise from that of the sea than in 



6 Phil. Mag. January 1870, p. 6. 



7 Phil. Mag. September 1865, p. 240. 



8 Phil. Mag. February 1860, p. 96. Prof. Challis says, "The mass of 

 the earth, taken as a whole, must be regarded as a fluid .... The effect of 

 internal pressure would cause the distinction between solidity and fluidity 

 to cease, probably at no great depth." 



Phil. Mag. S.4. Vol. 39. No. 260. March 1870. N 



