490 
Proceedings of the Royal Society of Edinburgh. [Sess. 
St Andrews the manuscript of the article “ Electricity ” must have been in 
the printer’s hands. The volume containing this article appeared in 1878. 
When in 1879 Chrystal became a candidate for the chair of Mathematics 
in the University of Edinburgh, Maxwell strengthened his former testi- 
monial by adding these words : “ I think it is of the greatest importance 
that, in a university in which the time that the majority of students can 
give to mathematics is so limited, their attention should be specially directed 
to those branches which will be most useful to them in their subsequent 
study of natural philosophy. This has always been kept in view in the 
University of Edinburgh. . . . That Professor Chrystal is well qualified 
to maintain the old reputation of the University is amply shown by the 
article ‘ Electricity.’ ... I have reason to know something of the amount 
of matter which must be gone through in order to write such an article, 
and of the difficulty of co-ordinating it, and I can confidently assert that 
the manner in which Professor Chrystal has made use of this mass of 
matter shows that he has the power, so invaluable in a professor, of giving 
such an account of what has been done in any subject as will give his 
students the greatest advantage in dealing with it themselves.” 
The article “ Electricity ” was followed in due course by the supple- 
mentary article “ Magnetism,” and the two are best considered together. 
In gathering material for these and other contributions to the Encyclo- 
paedia Britannica, Chrystal spared no pains in getting access to original 
sources. With unerring discrimination he sifted out from the mass of 
accumulated and rapidly accumulating experimental results those which 
were essential in the progress of our knowledge of electrical science. Not 
only are the articles compact history, but the varied experience of all 
types of scientific investigator is woven into a unity under the formative 
influence of Faraday’s conceptions and Maxwell’s fruitful methods. Theory 
and experiment go hand in hand. Where necessary, mathematics of a high 
order are introduced ; but the student not familiar with higher mathematics 
has no difficulty following the general argument and appropriating for his 
own purposes both the methods and the best results of experiment. In 
short, as an exposition of the development of the sciences of electricity and 
magnetism down to the date of publication, these two articles, concise and 
clear cut in their literary form, have never been surpassed for thoroughness 
of treatment, clearness of vision, unity of plan, and lucidity of expression. 
They at once became the English text-book for all real students of electricity 
and magnetism. 
In addition to these two great articles, Chrystal also wrote for the Ency- 
clopaedia Britannica the articles “ Electrometer,” “ Galvanometer,” “ Gonio- 
