I am looking for the source and context of this quote, found e.g. at [St Andrews](http://mathshistory.st-andrews.ac.uk/Biographies/Rudio.html):



> 
> Only with the greatest difficulty is one able to follow the writings of any author preceding Euler, because it was not yet known how to ***let the formulas speak for themselves***. This art Euler was the first to teach.  
> 
>  — F. Rudio
> 
> 
> 


(My emphasis. Slight variants suggest that it could originally have been in another language.)



Source of a quote by Ferdinand Rudio
The quote is from a speech Rudio gave at the Town Hall in Zürich on the 6th December 1883; The German original is published in Felix Stähelin, *Reden und Vorträge* (1956, I have not found it online). 


An English translation of the full speech is [here.](http://mathshistory.st-andrews.ac.uk/Extras/Rudio_Euler.html) The translated quote reads as follows:



> 
> But I cannot move on from reviewing Euler's mathematical work without
>  having considered an important factor. I have said that mathematics is
>  a language in which natural phenomena can be described in the simplest
>  and most comprehensive manner. With this in mind, you will understand
>  how important it is to express mathematical thoughts themselves as
>  concisely and clearly as possible. In this respect, Euler's work was
>  epoch-making. We can be safe to say that the whole form of modern
>  mathematical thinking has been created by Euler. If you read any
>  author immediately before Euler, it is very difficult indeed to
>  understand his terminology, as he has not yet learned how to let the
>  formulas speak for themselves. This art was not taught until Euler
>  came along.
> 
> 
> 


