VOL. LXXX.] PHILOSOPHICAL TRANSACTIONS. 6fll 



mortification to be thrown into the latter season of the year, as it could not be 

 placed on Goudharst steeple before the 9th of August 1788. Having finished 

 the few remaining observations, the paper proceeds to state the manner in which 

 the calculations are made, and the account drawn up in several sections, viz. 



Sect. 1. Description of the apparatus made use of in the measurement of the 

 base of verification in Romney Marsh, with the hundred-feet steel chain, in the 

 autumn of 1787, with the result of that operation, 2. General description of 

 the great instrument with which the angles in the recent trigonometrical opera- 

 tion were observed; showing also its various adjustments for practice. 3. De- 

 scription of various articles of machinery made use of in the course of the trigo- 

 nometrical operation. 4. Calculation of the series of triangles extending from 

 Windsor to Dunkirk, by which the geodetical distance between the meridians of 

 the Royal Observatories of Greenwich and Paris is determined. 5. On the dif- 

 ference between horizontal angles on a sphere and spheroid. 6. Manner of de- 

 termining the latitudes of the stations. Application of the pole star observations 

 to computations on different spheres, and also on M. Bouguer's spheroid, for the 

 determination of the difference of longitude. Ultimate result of the trigono- 

 metrical operation, by which the difference of the meridians of the Royal Obser- 

 vatories of Greenwich and Paris is determined. 7- An account of the observa- 

 tions made during the course of the trigonometrical operation for the determi- 

 nation of terrestrial refraction. 8. Secondary triangles, subdivided into 2 sets, 

 for the improvement of the maps of the country, and the plan of the city of 

 London and its environs. And the conclusion, containing propositions for ex- 

 tending trigonometrical operations over Great Britain. 



On several accounts it is not necessary to enter into the particulars of this ex- 

 tremely long and very detailed account of the measurements and calculations of 

 this important and extensive survey; particularly as this, and the former years 

 operations of this kind, have been collected into volumes, and published sepa- 

 rately, by Mr. Faden at Charing Cross; and also as it is stated by the b. s. in an 

 appendix to this paper, that very numerous and great errors have been committed 

 in the calculations, &c. so as to render the recomputation and reprinting of 

 many sheets unavoidably necessary. This circumstance is thus stated by Dr. 

 Blagden, one of the secretaries of the b. s. in the appendix, at p. 59 1. 



'* Our late much respected colleague. Major-general Roy, having finished, in 

 September 1788, the trigonometrical measurement described in the first part of 

 this volume, returned to London in a very indifferent state of health. From this 

 time he employed all the leisure that his illness, and his various official avocations, 

 allowed, in preparing the account of his operations, to be laid before the r. s. 

 But toward the autumn of 17S9 his infirmities increased so much, that the me- 

 dical gentlemen he consulted advised him to spend the following winter at Lisbon, 



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