MULL. METEOROLOGY. BAROMETER. 549 



vations, as the general result was similar ; and shall only 

 further remark, that on comparing the register of Green- 

 wich with that of Gordon Castle in Moray, some differ- 

 ences were found amounting to 0,8 ; the barometer at the 

 former station being in that case the lowest. The differ- 

 ence of level between these stations is trifling, and this 

 observation particularly serves to show that the rule re- 

 specting latitude is far from absolute. 



It can admit of no doubt that these irregularities depend 

 on analogous changes in the atmospheric pressure ; as it 

 will shortly be seen that they far exceed the limits of any 

 sources of error from construction or temperature. Whe- 

 ther they are connected with the direction of the winds 

 cannot be determined, from the want of sufficient mete- 

 orological observations ; but this is probable, from the 

 circumstance of their occurring most frequently in stormy 

 weather or at the times of the greatest changes of pressure. 

 The practical conclusions to be drawn from them are ; that 

 contemporary observations for the determination of altitudes 

 are least worthy of reliance in proportion to the horizontal 

 distance of the stations ; and that observations which are 

 not contemporary are not to be depended on absolutely, 

 because one of the observed instruments has for a given 

 time maintained a steady elevation ; since the correspond- 

 ing one may have nevertheless undergone considerable 

 fluctuation. 



It is now necessary to inquire respecting the differences 

 and irregularities above alluded to as arising from errors 

 of different descriptions in construction, and from other 

 disturbing causes ; for the purpose of determining to what 

 extent they detract from the above conclusions, and how 

 far they affect the accuracy of the instrument as a measure 

 of altitudes. 



A limited quantity of similar disagreements was found 

 on trial to take place among several barometers at very 

 short distances ; but they were very trifling when the 



