206 Dr. Bostuck's Observations on [March, 



of barometers in or near London, as well as some that were kept 

 at Edinburgh and at Perth, he perceived that they frequently 

 differed from each other to the amount of several hundredths of 

 an inch ; and as Dr. M'Culloch's object in the investigation was 

 to determine how far the barometer could be correctly employed 

 for the measurement of heights, he concludes that it is very 

 imperfectly adapted for this purpose. As to the cause of these 

 differences, Dr. M'Culloch draws an inference, directly the 

 Teverse of that which I had formed, that they depend not upon 

 the imperfection of the instrument, but upon actual differences 

 in the weight of the atmosphere in situations very contiguous to 

 each other. Dr. M'Culloch conceives that he has established 

 the four following positions : 



1. That the differences between barometers placed at two 

 stations, more or less distant one from the other, are more remark- 

 able at those times when the mercurial column experiences rapid 

 or considerable fluctuations. 



2. That the want of contemporary elevation or depression in 

 the two distant stations is the immediate cause of the observed 

 differences. 



3. That these differences will in general be as much greater 

 as the instruments on which the observations are made are more 

 remote from each other, supposing the observations to be con- 

 temporary. 



4. That in all cases the observations which are not contem- 

 porary deserve little confidence, although one of the barometers 

 should have remained for a considerable time stationary, since 

 the other may have experienced fluctuations during the same 

 period. 



I think it will be difficult to reconcile these positions with the 

 observations that are stated in my paper, or that the difference 

 of atmospherical pressure at Plaistow and at Clapton, or, still 

 more, in different parts of the Strand, can be adequate to produce 

 the variations that were indicated by the barometers in these 

 several stations. And the same conclusion is further confirmed 

 by the experiments that the editors of the Bibliotheque Uni- 

 verselle report as having been performed on this subject by M. 

 Ramond, in the neighbourhood of Clermont. With the same 

 object in view that induced Dr. M'Culloch to examine the 

 subject, in order to ascertain how far the barometer was to "be 

 depended upon as a correct instrument for ascertaining compa- 

 rative heights, M. Ramond placed six barometers in situations 

 not far from each other, used every necessary precaution in 

 making his observations, and applied the necessary corrections. 

 The horizontal distance of the stations varied from about 3,000 

 yards to 12,000 yards ; and some were placed at an elevation of 

 above 2,000 feet above Clermont. Fifty-three observations were 

 then made ; by comparing the height of the mercury in the 

 different stations with what the height of these different stations 



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