40 ENVGLISH MEN OF SCIENCE. [CAP.
trial, owing to the impossibility of obtaining good historical portraits. The value of these is further diminished by the passion of distinguished individuals to be portrayed in uniforms, wigs, robes,
or whatever voluminous drapery seems most appropriate to their high office, forgetting that all this conceals the man. The practice might well become common of photographing the features from different points of view, and at different periods of life, in such a way as would be most advantageous to a careful study of the lineaments of the man and his family. The interest that would attach to collections of these in after-times might be extremely great.
Thirteen families have been selected, out of those to which about 120 of the scientific men on my list belong, as appearing noteworthy for their richness in ability during two, three, or more generations, or for any other peculiarity ; in some cases they are also remarkable for purity of type. The facts may for the most part be verified by re-