On the different Theories of Arches, Faults, &c. 387 



seconds in the obliquity. Notwithstanding, should any 

 gentleman require the above two parts of the Nautical Al- 

 manac, for the use of his own observatory ; whether for 

 the correction of the tables, or the convenience "of setting 

 his instrinnents ; I should recommend him to avoid the 

 labour of calculating the same from the solar tables; where- 

 by he might fail into a greater error, unless he should em- 

 ploy several computers. In that case, he might safely de- 

 pend on the sun's longitude given in the Nautical Almanac, 

 and, allowmg for his difference of meridian from Greenwich, 

 with the apparent obliquity of the ecliptic so corrected, find 

 the true right ascension and declination of the sun. In- 

 deed, were he to profess to have made the original calcula- 

 tions, and these were to agree relatively with those oi the 

 Nautical Almanac, he would be suspected of having used 

 the same plagiarism which is ascribed to the French and 

 American astronomers in their publications. 



With respect to the Co)inoissmice des Tems, the compilers 

 acknowledge that they have depended on the calculations 

 published in the Nautical Almanac; haying on former oc- 

 casions found them correct. From the superior industry 

 of the French rtiathematicians, the Solar and Lunar Tables 

 have been constructed ; although the theories thereof have 

 been princi|}ally confirmed by the numerous and accurate 

 observations of the sun and moon, which have been made 

 at Greenwich, during a long series of years, with the greatest 

 skill, and the best instruments that have been hitherto pro- 

 duced. 



I am, sir, your obedient servant, 



Blackheath,Nov. 15, 1811. S. GrOOMBRIDGE. 



LXX. Some Account of the different Theories of Arches 

 or Faults, and of Domes, and of the Authors who have 

 written on this most delicate and important Application 

 of Mathematical Science. Bij a Correspondent. 



P ROM the general history of the progress of the inquiries 

 into the theories of the equilibration of vaults, it will be - 

 seen, how important the subject has been considered by those 

 who have not been architects, but have attained the highest 

 eminence in maiheuiatical and mechanical science. In 

 reading t'.iis history of coatrarious results, and in surveying 

 and turning in the mind the vaults now subsisting, the 

 productions of aichitects unacquainted with the present 

 theories, much caution is ncccbsary, lest the conclusion 

 libs ■ be 



