In the case of the descriptive natural sciences, the Latin names of the genera and species, the Latin nomenclature of anatomy and other similar groups, form a common international possession. Physiology, biology, sociology, as well as history and ancient philology, possess as yet, however, no system of internationally intelligible terms. In modern philology (phonetics) practical endeavours have already been made to construct an international system of sound symbols. All these sciences possess naturally the designation of numbers by means of numerals which have a perfectly international character. Since in mathematics not only the quantities, but also the operations, are denoted by universally understood symbols, it is already possible, with comparatively few additions, to express long trains of mathematical thought in a manner which is internationally intelligible, that is, intelligible to those who are acquainted with the science and its symbols. For a considerable time Professor Peano, in Turin, has been publishing works written in this manner. We perceive here the realisation of the ideal of a purely ideographic language, which can be read by the specialist without his requiring to translate it into the words of any particular form of speech. To quote a similar example from chemistry, J. H. van't Hoff, in one of the publications of his youth, avoided assigning names to the chemical substances with which he dealt, considering that his meaning would be much better conveyed by the corresponding structural formulæ. Such a text would be quite intelligible to a trained chemist without the formulæ calling up in his mind any particular words, indeed without any such words existing at all. These well-known facts show _that the problem of an international language has already been partly solved in science_. In so far as definite and fairly stable concepts have been formed in science, they may be designated by arbitrary symbols, which may if necessary be universally accepted and understood. Hitherto such symbols have been mainly employed for reading, that is to say intended for the eye, and not for the voice and ear. For example, in different languages quite different sounds are assigned to the numerals, so that, whilst the written symbols are universally intelligible, the spoken ones are not.