2QQ On the Arcs perpendicular to the Meridian, 



teen and seventeen degrees. From this portion, therefore, we 

 can draw no conchision whatsoever. 



We are informed by Colonel Bonne, that the difference of 

 tlie meridians between Strasbourg and Paris, computed from the 

 triangles on the assumed ellipticity of ^i^, amounts to 21' 

 35",88 ; in which estimate we are enabled, in the manner before 

 noticed, to acquaint ourselves with the value of the arc in metres 

 from which it was originally made. The first attempt to ascer- 

 tain the celestial amplitude of this arc was made in 1824, under 

 the direction of Colonel Henry, when, of one hundred signals, 

 six only were transmitted throughout the line, viz., three on the 

 25th of August, and three on the 26th. The six transmissions, 

 however, presented so satisfactory an accord with each other, 

 that, in the first of the two memoirs published by Colonel 

 Bonne, in the Memorial Topographique et Militaire, namely, in 

 the one which records the proceedings up to the end of 1824, 

 the presumption is expressed, that the mean result so obtained 

 would scarcely be altered by a new attempt. The attempt was, 

 however, renewed in the following year, under the direction of 

 Colonel Bonne, Colonel Henry being dead intermediately, when 

 the result of that year was proved to differ nearly eight-tenths 

 of a second from that of the preceding year ; of which it is 

 stated in explanation, in the second memoir of Colonel Bonne, 

 that the unfavourable weather of the preceding year had not 

 permitted Colonel Henry to ascertain the correction of his clock 

 with sufficient exactness. We have been induced to notice this 

 circumstance, because it strengthens our view (to which we shall 

 presently advert) of the expediency of providing some check, 

 at least, upon the total arc. It would have been hard to have 

 judged that an amplitude derived from the observations of two 

 different days, the partial results of which, as well as the mean 

 of each day, presented so satisfactory an accord, and in the 

 report of which no circumstance indicative of doubt was men- 

 tioned, was inferior to other determinations, especially on the 

 parallel of 45®, which have not been so tested by repetition : 

 nevertheless, the error that repetition in this case discovered, 

 was of a magnitude that, distributed on the whole extent of the 

 arc, from Brest to Czernowitz, would still have very materially 

 influenced the ultimate conclusion, not less indeed than eight in 



