They afford a lesson to the modern metaphysical and recondite writers not to overvalue their works.

I suppose he must have been all right, because you don't half cop it for killing a soldier.

the warblings of birds in the hedgerows

The authors propose using polychoric correlations in order to estimate the correlation matrix before using PCA. Polychoric PCA assumes that the observed ordinal variable has an underlying continuous variable and uses maximum likelihood to calculate how that continuous value would have to be split up in order to produce the observed data.