It is required or supposed that every scholar or man of science should know at least German, French, and English. For the majority of German scholars and men of science this may hold good, but in the case of the French it is less true, and in the case of the English least of all. The knowledge of these three languages is, however, no longer sufficient, and that for the following reasons. In the first place, several other languages must be taken into account, for many Italians write only Italian, many Dutchmen only Dutch, whilst numerous Russians, Poles, Czechs, Hungarians, Scandinavians, and Spaniards employ only their national languages. In this way much escapes general knowledge and recognition, or is only accessible in a belated or mutilated form. In the second place, the difficulty of a quick mutual understanding is great, even for those who can command these three chief languages. If one is possessed of a little natural talent, one can by dint of industry and much loss of time easily get so far as to read or understand a paper or a letter in a foreign language, but when it comes to writing (replying) the task is incomparably more difficult. One can, however, not assume, when a German scholar or man of science replies in German to a letter written in French or English, that he will be always understood. The matter is much worse in the case of oral intercourse, especially at scientific congresses. At these the three chief languages mentioned above are usually now declared to be official, that is to say, permissible for the delivery of papers. As a matter of fact, however, the language of the country in which the congress is held usually dominates. The German speaks French in Paris, but the Englishman mostly only English, and demands, as occurred at the recent Refrigeration Congress in Paris, the translation into English of the papers read at the sectional meetings. Only very few can take part in the discussions, and many must be well content if they are able to understand the usually rapidly delivered papers. Many an important criticism is not made because one does not possess the expertness necessary for discussing a question in a foreign language, and does not wish to expose oneself to the chance of a rebuff, caused not so much by ignorance of the matter in hand as by want of facility in expression. Every member of a congress has noticed that whenever the language employed in the papers changes, a considerable number of the audience leave with more or less noise, in order to avoid being compelled to listen to a paper which they do not understand. Congresses would be certainly much better attended were it not that these difficulties keep many away.