At the time I entered the laboratory Williamson was engaged in the researches which have made his name a household word to chemists all the world over. His was a mind of great originality, and his personality was a most attractive one. And, despite his physical disabilities—for he lost an eye and the proper use of his left arm in early childhood—he was a diligent and accurate worker. Ardently devoted to his science, he infected all who worked under him with the same feeling. And his pupils willingly own that much of the success that they may have met with in after years was due to his teaching and example. I well remember the feelings of interest he aroused as he each day came down to the laboratory brimful of new ideas. First it was his explanation of the theory of etherification, of which he proved the truth by preparing the mixed ethers, thereby ascertaining the general constitution of alcohols and ethers, and laying one of the foundation-stones of modern chemistry. Next it was his well-known paper on the constitution of salts, in which he enunciated principles which have since been generally adopted. Then came his views on atomic motion and interchange, the first definite statement of a series of chemical phenomena which in the hands of Van ’t Hoff and others have become of the highest import.… He clearly foresaw the principles upon which the modern development of the steam-engine depends, and though he failed for want of constructive skill, he pointed the way which engineers have since followed with conspicuous success. In his second year in the Birkbeck Laboratory Roscoe became Williamson’s private assistant, and took part in his researches, and when Graham accepted the Mastership of the Mint, and Williamson succeeded to the chair at University College, Roscoe was made lecture assistant. Williamson had the idea at that time of publishing an abridged translation of Gerhardt’s _Chimie Organique_, for the benefit of English students, which Roscoe was to prepare, but nothing came of the project. Graham, who had been commissioned to send out an assayer to the Sydney Mint, offered Roscoe the position. The salary was very tempting, but as his mother and sister had no desire to go to Australia, the offer was declined, and his cousin Stanley Jevons, who had passed through the Birkbeck Laboratory, was sent in his stead. It was in recognition of Roscoe’s association with Williamson that nearly forty years afterwards he was deputed, on behalf of the subscribers, to present the portrait of his master which now hangs in University College.