274 Mr Galbraith on the English Arc of the Meridian. 



These remarks of Captain Kater have been verified by my 

 own experience, and there is no probable way of obviating the 

 effects of refraction on horizontal angles, but by combining 

 the French method of repetition with our own more powerful 

 instruments on different days under various atmospheric cir- 

 cumstances. 



ADDITIONAL NOTE. 



The following remarks have been occasioned by the receipt 

 of a part of the Ordnance Survey, since the original paper 

 was delivered to the Secretary : — 



After a lapse of tliirty years, the publication of the results of the Ord- 

 nance Trigonometrical Survey of Britain has been resumed. This has 

 been recommenced by the pubhcation of a part, titled, " Astronomical 

 Observations, made with Ramsden's zenith sector, together with a Cata- 

 logue of Stars which have been observed, and the amplitudes of the celes- 

 tial arcs, deduced from the observations at the differeat stations ; and 

 published by order of the Board of Ordnance." 



Of this work a few copies have been distributed, by presentation, to 

 different individuals, and it is but justice to those employed, to affirm, 

 that all the deductions are made according to the best methods now used 

 in that branch of science. Colonel Colby, the indefatigable conductor, 

 has availed himself of the advice of Mr Airy, the astronomer-royal ; and 

 Lieutenant Yolland, of the Royal Engineers, under the Colonel, has fol- 

 lowed up this advice with diligence and care. 



The points of which the latitudes and intermediate arcs of the meridian 

 are here given, are Dunnose in the Isle of Wight ; Greenwich Observa- 

 tory ; Clifton Beacon in Yorkshire ; Arburyhill in Northamptonshire ; 

 Deiamere Forest in Cheshire ; Burleigh Moor in Yorkshire ; Kellie Law 

 in Fifeshirc ; Cowhythe hill in Banffshire ; and, lastly, the station on the 

 small isle of Balta in Shetland, comprehending an arc of the meridian 

 passing from the southern extremity of Britain, to the more northerly of 

 the islets belonging to it, amounting to above ten degrees, or about one- 

 ninth part of the quadrantal arc of the meridian from the equator to the 

 pole. This will not only be a most valuable operation for improving the 

 ccography of the country, — a thing much wanted from the great inaccu- 

 racy of our maps and charts, but a valuable contribution also to astrono- 

 mical and geodetical .'cience. We are informed by the Colonel towards 

 the close of his preface, — " That the terrestrial observations requisite to 

 enable me," says he, " to complete and publish the geodetic distances 

 connected with the astronomical results, are now in so advanced a state, 

 that the printing of them will shortly be commenced." These being com- 

 pared with others of a similar kind in different parts of the world, will 

 enable him to deduce a proper value of the earth's axes, and thence to fix 



