12 
Proceedings of the lioyal Society 
floating somewhat dimly before the eyes of mathematicians for 
half a century, and was just then beginning to assume a living 
form in the mind, and a living exponent, though a somewhat 
obscure one, in the writings of Sir W. R. Hamilton. It was not 
until six years later that the doctrine of Quaternions of the great 
master, as developed in his u Lectures,” swallowed up in its vast 
amplitude all that had preceded it. Terrot must accordingly be 
considered as one of the pioneers of the science. In the paper 
now referred to he points out the applicability of the method to 
plane trigonometry in all its parts ; but he could see his way no 
further. Years after, when paralysis had laid him low, on being 
told that Symbols of Direction had been embodied by Sir William 
Hamilton into the full-grown science of Quaternions, his delight 
was expressed in the form of thankfulness that enough of life had 
been spared him to know that the dream of his early years had 
been realised, even although all power to comprehend it had 
passed away from him. 
In 1858 Bishop Terrot published in our Transactions a paper 
“ On the Possibility of Combining two or more Probabilities of 
the same Event, so as to form one Definite Probability.” This 
paper was his best contribution to mathematical science. In 
addition to its own excellence, it has the merit of having drawn 
forth the valuable paper of the late Professor Boole, “ On the 
Application of the Theory of Probabilities to the Question of the 
Combination of Testimonies or Judgments,” to which the Council 
of this Society awarded the Keith medal in 1858. In this paper 
the conclusions of Bishop Terrot are confirmed, and a flood of new 
light is cast on the subject. It ought perhaps to be added, that 
an extended correspondence between the Bishop and Boole had 
preceded the publication of the papers in question ; in which the 
Bishop had steadily manifested an anxious desire both to promote 
the advance of science, and to aid Boole in his upward career. 
Selfish ends had no place in the Bishop’s mind. 
In dismissing this brief notice of Bishop Terrot’s scientific 
connection with the Royal Society, it may not be amiss to add a 
word or two on his personal connection with us. For many years 
of his life he was one of the regular attendants of our meetings ; 
and when not actively engaged in the work going on, he was an 
