Mr. Ellis commenced as follows:— ‘By intonation is here meant a selection of musical sounds of certain degrees of pitch, made according to some fixed principle. It is called just, when that principle is to make the consonances as perfect as possible. It is called tempered, when the degrees of just intonation are slightly altered, with a view of materially facilitating performance on instruments having fixed tones, and, since the introduction of harmony, with the intention of injuring the consonances as little as may be compatible with that facilitation. That is to say, just intonation prefers harmony to manipulation—tempered intonation prefers manipulation to harmony. To understand this distinction thoroughly, and the various contrivances that have been proposed for serving at once the muse and the instrumentalist, it is necessary to know on what consonance and its deterioration depend. This requires a knowledge of the nature of musical sound itself, such as has been collected and clearly explained, within the last thirteen years, by Professor Helmholtz. But the results may be readily felt and appreciated by simply hearing a few experiments and harmonies. It seemed to me, therefore, that I should be rendering a service to the Musical Association if I showed a few of the elementary experiments in a manner which anyone could reproduce for himself, and also exhibited the effect of the principal tempered intonations, as contrasted with the just, in the chief forms of harmony. In doing so, I shall endeavour to reduce my observations to the merest thread sufficient to string my illustrations together, and refer those who wish to enter fully into the subject to my translation of Professor Helmholtz's work on the Sensations of Tone.’