148 Proceedings of Royal Society of Edinhurgh. [jan. 30 , 
side of the layer precisely as the first would have done had it escaped 
collision^ Of course it would be easy to make a 20 page proof 
of this by tbe help of an imposing array of multiple integrals. 
But this would be the sort of thing which I have called 
“ playing with symbols,” i.e. using them instead of thought^ 
while their proper function is to assist thought. A mathematical 
demonstration does not necessarily imply the use of symbols, 
any more than that of diagrams : — and, when we find an author 
continually using symbols to establish what is obvious without them, 
we very naturally question the validity of his symbohcal processes 
when they are employed for their legitimate purpose. I still think 
the assumption above a legitimate and indeed almost an obvious 
one ; but it is strange that an objection of this kind should come 
from a writer like Prof. Boltzmann, who (see head Second above) 
has made, and still defends, a fundamental assumption (of the 
class to which he applies the term “ unbewiesene Voraussetzung ”) 
which most clamantly demands proof. 
Finally, as Prof. Boltzmann objects alike to Greek, and to English, 
quotations, although they have Plato and De Morgan for their 
authors, what does he say to the Latin one 
“ Quis tulerit Gracchos de seditione qiierentes'^ % 
PRIVATE BUSINESS. 
Eudolph Julius Emmanuel Clausius, Professor of Natural Philo- 
sophy in the University of Bonn; Ernest Haeckel, Professor of 
Zoology and Histology in the University of Jena; Demetrius 
Ivanovich Mendeleff, Professor of Chemistry in the University ofK|j 
St Petersburg, who had been proposed as Foreign Honorary Fellows, If I 
and had been named from the Chair in terms of Law XIL, at theS; 
Meeting of 5th December 1887, were balloted for, and declared'" 
duly elected Foreign Honorary Fellows of the Society. 
