[Footnote 192: Geol. Essays, p. 441.] The appeal made here to Frisi is singularly unfortunate, as that philosopher has demonstrated the very contrary of Mr Kirwan's position, and has proved, that the disturbance given to the diurnal motion by the causes here referred to may be real, but cannot be perceptible. Having investigated a formula expressing the law which all such disturbances must necessarily observe, he concludes, "Hàc autem formulâ manifestum fiet, ex iis omnibus variationibus quæ in terrestri superficie observari solent, montium et collium abrasione, dilapsu corporum ponderosiorum in inferiores telluris sinus, nullam oriri posse variationem _sensibilem_ diurni motûs. Nam si statuamus data aliqua annorum periodo terrestrem superficiem ad duos usque pedes abradi undique, eam vero materiæ quantitatem ad profunditatem pedum 1000 dilabi; erit omne quod inde orietur incrementum velocitatis diurni motûs 30000/(19638051)^2 = 1/12855068184."[193] [Footnote 193: Frisii Opera, tom. iii. p. 269.] Here, it is evident, that Frisi admits those very changes on the surface which we are contending for, and shows, that their tendency is to accelerate the earth's diurnal motion, but, by a quantity so small, that, in a space of time amounting at least to 200 years, the increase of the diurnal motion would only be such a part of the whole as the preceding fraction is of unity.[194] [Footnote 194: The time requisite for taking away by waste and erosion two feet from the surface of all our continents, and depositing it at the bottom of the sea, cannot be reckoned less than 200 years. The fraction 1/12855068184, reduced to parts of a day, is 1/148554 of a second; so that it would require 200 years to shorten the length of the day, by the above fraction of a second; and therefore it would require 148554 times 200 years, or 29710800 years, to diminish it an entire second. The accumulated effect, however, of all the diminutions during that period, would amount to much more: and if we had any perfectly uniform standard to compare the motion of the earth with, its difference from that standard would increase as the squares of the time, and the total acceleration would amount to one second in 77080 years. Whatever relation this bears to the age of the globe itself, it exceeds more than ten times the age of any historical record.