Biometrika, Vol. X, Parts II and III 
Plate XIX 
Moilel of Eegressioii Siuface, giving mean Aveiglit of Girls of Class B of Glasgow Schools for a given 
Height and Age. The mean weight is the vertical coordinate and each section parallel to the front 
of the model gives the mean weight lor the several Heights of Girls of a given Age. See p. 295. 
