JANUARY 15, 1914] 
NATURE 559 
of the picture, and there are certain periods in 
the history of art during which for a considerable 
length of time there was no change in the artist’s 
palette. It is necessary, therefore, to bring other 
methods as well to bear upon the problem. One 
of these is the study of mediums used at different 
dates, and in this study sufficient progress has 
been made to prove it of use for dating purposes. 
But, as will be obvious to a chemist, the analytical 
difficulties here are much more serious. 
The microscopic study of pictures by magnify- 
ing under low powers revealed remarkably dis- 
tinctive characters in the artists’ brushwork; and 
the more pictures examined, the more valuable 
did the method appear as a trustworthy means of 
and a drawing of lines which are themselves in 
some cases not more than one-tenth of a milli- 
metre in diameter, and yet are put in with perfect 
certainty. The study of foliage is also of special 
interest, as each man’s method of handling foliage 
is characteristic. 
Among the large number of photographs taken 
it is difficult to know which to select as examples 
of the method, but probably those will be of 
most interest which illustrate an actual problem. 
Such a problem is offered by the picture in the 
National Gallery known as ‘The Old Gray 
Hunter,” which is signed ‘‘ Paul Potter,” and has 
been stated by no less authority than Dr. Bredius 
to have been painted by Verbeecq, a contemporary 
’ 
Fic. 1.—Brushwork of the head of a cow in an undoubted picture by Paul 
Potter in the National Gallery. 
determining the authorship of a picture. There 
are probably certain schools of art to which the 
method does not apply. A great deal of the 
sixteenth-century Italian work, for instance, is 
handled in a very similar way, and it may be 
very difficult to apply this method successfully to 
some of these painters. But there is a wide field 
in which the artist has left his individual mark 
upon his paint, and has so drawn for the future a 
signature which it is impossible to forge. One 
of the most interesting revelations is that many 
of these touches are so fine as to be really beyond 
the limit of unaided sight. For instance, the 
brushwork of Teniers and of Watteau can be 
magnified up to four or five diameters, revealing 
an accuracy of touch and a delicacy of modelling 
NO. 2307, VOL. 92] 
Fic. 2.—Brushwork of the head of the horse in “‘ The Old Grey Hunter,” 
shown by the touch not to be by Verbeecq, and inferior to Paul Potter's 
best work. 
artist. There is another Paul Potter in the 
National Gallery (No. 849), the authenticity of 
which has never been questioned, and which a 
comparison of photomicrographs with photo- 
micrographs of a pedigree Paul Potter in The 
Hague Museum shows to be genuine. 
The first photograph here reproduced (Fig. 1) is 
the head of a cow in this genuine Paul Potter 
for the comparison with the head of the horse 
(Fig. 2) in “The Old Gray Hunter.” It is at 
once obvious that, while there are certain simi- 
larities in the brushwork, the painting of the 
horse’s head is by a very inferior hand to that 
of the painting of the cow. The probability is, 
then, that it is not Paul Potter’s work, although 
this cannot be considered as absolutely proved. 
