5.54 JEAN-BAPTISTE-ANDRl^ DUMAS. 



he exhibited such relations, especially triads of elementary substances; 

 such as chloriue, bromine, and iodine ; oxygen, sulphur, and selenium; 

 phosphorus, arsenic, and antimony; calcium, barium, and strontium: 

 in which not only the atomic weight, but also the qualities of the 

 middle member of the triad, were the mean of those of the other two 

 members. Later, he came to regard these triads as parts of more ex- 

 tended series, in each of which the atomic weights increased from the 

 first to the last element of the scries, by determinate, but not always 

 by equal differences, the values being, if not exact multiples of the 

 hydrogen atom according to the hypothesis of Prout, at least multi- 

 ples of one half or one quarter of that weight. There can be no 

 doubt that these speculations were more fanciful than sound, and that 

 Dumas did not do full justice to earlier theories of the same kind ; but 

 with him these speculations were merely the ornaments, not the sub- 

 stance of his work, and they led him to fix more accurately the con- 

 stants of chemistry, and thus to lay a trustworthy foundation upon 

 which the supersti'ucture of science could safely be built. 



That exuberance of fancy to which we have referred made Dumas 

 one of the most successful of teachers, and one of the most fascinating 

 of lecturers. It was the privilege of the writer to attend the larger 

 part of two of his courses of lectures given in Paris iu the winters of 

 1848 and 1851, and he remembers distinctly the impression pro- 

 duced. Besides the well-arranged material and the carefully pre- 

 pared experiment, there was an elegance and pomp of circumstance 

 which added greatly to the effect. The large theatre of the Sorbonue 

 was filled to overflowing long before the hour. The lecturer always 

 entered at the exact moment, in full evening dress, and held to the 

 end of a two hours' lecture the unfliigging attention of liis audience. 

 The manipulations were entirely left to the care of a number of as- 

 sistants, who brought each experiment to a conclusion at the exact 

 moment when the illustration was required. An elegance of diction, 

 an appropriateness of illustration, and a beauty of exposition, which 

 could not be excelled, were displayed throughout, and the enthusiasm 

 of a French audience added to the animation of the scene. 



To the writer the lectures of Dumas were brought in contrast to 

 those of Faraday. Both were perfect of their kind, but very different. 

 Faraday's method was far more simple and natural, and he excelled 

 Dumas in bringing home to young minds abstruse truths by the logic 

 ot veil-arranged consecutive experiment. With Dumas there was no 

 attempt to popularize science ; he excelled in clearness and elegance of 

 exposition. He exhausted the subject which he treated, and was able 



