ttm\f:n6w measurihg on the Continent 199 



tied to the more consideration, since tlie invention of Mr. Drum- 

 mond's lamp, employed since 1825 in the geodesical operations 

 in Great Britain, the light from which, compared with the light 

 from M. Fresnel's, is in the proportion of 20 to J . 



We come now to the consideration of the ellipticity with which 

 the measurements on this parallel correspond, so far, at least, 

 as the authorities of which we have spoken enable us to draw a 

 conclusion. Commencing with the arc between Buda and 

 Munich, as the most easterly of which we have any particulars 

 whatsoever, we are informed by M. Littrow (Corr. Ast. Zach. 

 1. c.) that the geodesical distance measured between the obser- 

 vatories of Buda and Vienna, calculated on an assumed ellipti- 

 ticity of -^-fj, was found equal to a difference of meridians of 

 10' 41",292 ; and that the distance measured between Vienna 

 and Bogenhausen (near Munich), computed on the same 

 assumed ellipticity, was found equal to 19' 05",26 ; making 

 together a geodesical amplitude between Buda and Bogen- 

 hausen, of 29' 46",552, on the supposition of the ellipticity 

 being -^jj. It is not difficult to learn from hence the value of 

 the arc in metres from which this deduction must have been 

 derived : by combining this number of metres with the true 

 difference of meridians, or the celestial amplitude obtained by 

 the fire-signals, 29' 45",9, we obtain the value of a mean 

 degree of the parallel ; by combining this again with the mean 

 degree of the meridian between Greenwich and Formentera, 

 we find that the operations on the parallel between Buda and 

 Munich, taken in concert with those between Greenwich and 

 Formentera, correspond to an ellipticity of -^-l^. 



We find in Colonel Bonne's report the celestial arc between 

 Bogenhausen and Strasbourg, 15' 29",42, apparently the most 

 satisfactorily determined of any of the portions on either of the 

 pamllels. Unfortunately, we are nowhere favoured with the 

 results of the corresponding geodesical measurement ; nor with 

 any deduction or inference, from which we might obtain it, by 

 treading back the steps of a calculation. This is the more to 

 be regretted, as it is the only result which is wanting to enable 

 the combination of the three portions, viz., between Paris and 

 Stmsbourg, Strasbourg and Bogenhausen, and Bogenhausen 

 and Buda, which would malie a connected arc of between six- 



