the Governmenl Trigonometrical Survey, 429 



person, too immediately dependent on Colonel M. as head of the 

 Woolwich AcademVj to have been by any means decent or pro- 

 per, in mv estimation, or that of many very competent persons, 

 with wh.om I liave conversed on the subject. 



'' From ha\ing, when in the late Duke of Bedford's employ, 

 paid considerable attention to the principles, practice and pro^ 

 gress of the Trig-. Survey, in and around Bedfordshire, and 

 having made a very great number of careful observations, with 

 €ach of the very admirable Theodolites they use, and recorded, 

 and applied these in a multitude of minutely accurate calculations 

 of intersecting Triangles, and having thus obtained the most 

 ample and satisfactory c/ieck<;, on the results as to J ngles (when 

 often enough observed) and lengths of calculated Lives, I am 

 able to concur most fully uith Don R. who has in another mode 

 gone over the whole calculations anew, that the net-work of 

 lines spread over the surface of our Island by this Survey (in- 

 cluding the measured bases) are of indispiitahle accuracy ; but 

 no persons, except some in the Woolwich Acad., who can be 

 deemed competent, will I think be found to say, that the other 

 imporioiU data, for turning this grand i^'urvey to the phj'sical or 

 philosophical uses of which it is susceptible, have yet been de- 

 termined, within any degree of corresponding or sufficient ac- 

 ciirncy, to these mere Lines, every three of them in different and 

 almost unknown planes, strictly speaking. 



" That is, as already (and secondly) observed, there is wanting, 

 the actual lieights of each Statif>n, with reference to a curved 

 surface of e'^uilibrinm (as yet, of tai known form, eK?iCi]\) formed 

 by the Sea, around our Island, and to other nearly similar and 

 parallel higher curved surfaces, inland, wliich are followed by the 

 several Canal-ponds (with some connecting leiw/lings, which are 

 wanting), in a connected net-work, over the Island's surface. 



" Fourth, The ascertaining, by very numerous repetitions^ 

 under proper and fully recorded circumstances, of heat, "pressure, 

 moisture, clouds, &c. the apparent angular elevation or depres- 

 sion, of each Station, with every other visible from it; with 

 much larger and belter Lntrumenls, than have yet been used 

 for this purpose ; two of which Instruments should, as often as 

 possil)le, be simultaneously used in observations, at each end of 

 a line between Stations. Calculations from these elevations and 

 depressions, would by comparison with the actual heights, fur- 

 nish data, now exceedingly wanted bv Astronomers and Trigo- 

 nometrical .Surveyors, for determining the Refractions at very 

 low elcvalions, some even below the liorizontal line (see Phil. 

 Mag. vol. xlvii. p. 2.'3) ; and other more considerable elevations, 

 between Church-Towers, &c, in valleys, near Canals, (already 



well 



