_Nature, Vol. 37 (1887-1888), p. 162._ =1043.= Tait dubbed Maxwell dp/dt, for according to thermodynamics dp/dt = JCM (where C denotes Carnot’s function) the initials of (J. C.) Maxwell’s name. On the other hand Maxwell denoted Thomson by T and Tait by T′; so that it became customary to quote Thomson and Tait’s Treatise on Natural Philosophy as T and T′.--MACFARLANE, A. _Bibliotheca Mathematica, Bd. 3 (1903), p. 189._ =1044.= In future times Tait will be best known for his work in the quaternion analysis. Had it not been for his expositions, developments and applications, Hamilton’s invention would be today, in all probability, a mathematical curiosity. --MACFARLANE, A. _Bibliotheca Mathematica, Bd. 3 (1903), p. 189._ =1045.= Not seldom did he [Sir William Thomson], in his writings, set down some mathematical statement with the prefacing remark “it is obvious that” to the perplexity of mathematical readers, to whom the statement was anything but obvious from such mathematics as preceded it on the page. To him it was obvious for physical reasons that might not suggest themselves at all to the mathematician, however competent.--THOMPSON, S. P. _Life of Lord Kelvin (London, 1910), p. 1136._ =1046.= The following is one of the many stories told of “old Donald McFarlane” the faithful assistant of Sir William Thomson. The father of a new student when bringing him to the University, after calling to see the Professor [Thomson] drew his assistant to one side and besought him to tell him what his son must do that he might stand well with the Professor. “You want your son to stand weel with the Profeessorr?” asked McFarlane. “Yes.” “Weel, then, he must just have a guid bellyful o’ mathematics!” --THOMPSON, S. P. _Life of Lord Kelvin (London, 1910), p. 420._ =1047.= The following story (here a little softened from the vernacular) was narrated by Lord Kelvin himself when dining at Trinity Hall:--