190 Mr J. D. FORBES on the Oscillations of the Barometer. 



EXPLANATION OF PLATE VII. 



THIS Diagram is intended to exhibit the curve by which the Horary Oscillation 

 of the Barometer is connected with the Latitude. 



The axis AX represents the quadrant of latitude extended into a straight line ; 

 and the distances of the points which are laid down on either side of it, give the 

 projections upon an arbitrary scale of the amounts of barometric oscillation. The 

 ordinates are reckoned plus to the right hand of the axis, and minus to the left. The 

 curve YM^ drawn through these points, gives the best expression of the law which 

 connects them, the sum of the squares of the deviations of the observed ordinates 

 from the computed ones being reduced to a minimum, as was shewn in the preced- 

 ing paper, this curve being merely a mechanical projection of the final equation. 



The amount of the equatorial ordinate AY is 2.650 millimetres. That of the 

 polar ordinate X y is 0.381 millimetres. The latitude at which the oscillation 

 changes its sign, or where the curve cuts the axis at M, is 64 8' 6". 



