28 



The only remaining operatiou is the détermination of the quantifcy (A— /2), 

 in order that [Ä^",J,„ may be computed by means of équation (15). The values 

 obtained for a, h, c, d, were: 



a = -0.81, ft = -2.61, c = + 0.66, fZ = +2.76, 



from a first series of observations. The corresponding corrections computed 

 by équations (14) were: 



for a, -0.15; for h, +6.59; for c, +1.05; for d, - 3.49; 

 giving 



(/'i -/.) = + o!9G 



A second series of observations, in which the points of the reseau next 

 to the extreme points were observed, gave: 



{fx -/.) = - l'"55 

 We hâve adopted as definitive the mean value: 



(/;-/2) = -o'.30 

 which corresponds to a value for the angle between the diagonals of: 



90» + (/) = 90«0'0".8 

 and substituting in équation (15) we bave: 



{K',l^ = \E:,l-QmSl (m -14) 

 Applying this correction to the value of [iTgi],, just computed, we hâve: 



-0.0087 (2 -14) = + 0.10 

 [Z"30, = + 3.39 



