'362 M. Delcros 1 Barometrical Measurement [Nov. 



The mean differences for the points marked in the last four 

 columns of the table are, 



Metres. , Metres. Metres. Metres. 



4-27 . . 3-84 8-01 2-25 



And in eliminating for Paris the last result, the difference of 

 which is — 18'61, evidently suspicious, we shall have for this 

 point 2*14. 



These results will be the more surprising, because the mean 

 disagreements are inversely as the horizontal distances ; because 

 these distances are very great ; and because the successive 

 observations are made at too great intervals from each other, 

 are too few, are made at times when the atmospherical disturb- 

 ances are great, and because they are almost always solitary. 

 Certainly all these causes united might have occasioned enor- 

 mous errors, and yet the agreement of the results does not 

 allow us to suspect their existence. Of how much importance 

 would such measurements be to general geology if they were 

 made to traverse whole continents. 



To point out the more clearly the advantages and the accuracy 

 of the barometer, I shall exhibit in the following table the series 

 of disagreements which affect the most accurate geodesical 

 measurements which have been executed in Europe since the 

 introduction of the circle of Borda, and the improvement of the 

 geometrical methods by Delarnbre. Surely no one will be 

 tempted to blame such observers, and to say that they were not 

 capable of doing better. If the great mathematicians who mea- 

 sured the meridian of Fiance, if we ourselves have not been able 

 to obtain better results, the reason is, that the nature of the pro- 

 blem does not admit of a greater degree of exactness. It would 

 be in vain to endeavour to come nearer the truth by multiplying 

 zenith distances, and then making a choice a posteriori to get 

 the results to agree. Such a method would be contrary to all 

 the principles of probability. It would be disagreeable to every 

 honest observer, and ought to be severely and absolutely banished 

 from geodesy. It may indeed flatter the pretensions of those 

 who would be thought to do better than any one else ; but it 

 will never impose upon philosophers. 



