Hearing, again by accident, that Professor Boltzmann has in the Vienna Sitzungsberichte published a new attack on my papers about the Kinetic Theory, I at once ordered a copy, which has at length arrived. As my papers appeared in our Transactions, I think my answer to this fresh attack should be communicated in the first place to this Society. The time I can spare for such work at this period of the year is very scant, and Prof. Boltzmann has raised a multitude of questions. I will take them in order. But I must commence by saying, with reference to Prof. Boltzmann's peculiar remarks on my behaviour as a critic, that, while leaving them to the judgment of readers, I shall have to bring before the same readers several instances in which Prof. Boltzmann has completely misstated the contents or the objects of my papers. This is not a new departure. In his first attack on me he said that I had nowhere stated that my investigations were confined to hard spherical particles; whereas I had been particularly explicit on that very point. But fresh cases of a similar character abound in this new attack.