104 



became vacant, by the appointment of Dr. Lloyd to a senior fel- 

 lowship, and Mac CuUagh was elected to it without opposition. 



These are the principal events and dates of a life spent in the 

 peaceful pursuits of learning, and in the diligent discharge of aca- 

 demic duties. In reviewing the labours which were the result of 

 that life, it will be necessary, in the first instance, to give some ac- 

 count of the papers published in the Transactions of this Academy, 

 containing the researches in Mathematical and Physical Science, on 

 which the fame of Mac Cullagh chiefly rests. 



His first papers were read here, before he had become a Mem- 

 ber of the Academy, and before he was elected a Fellow of the Col- 

 lege. They were communicated to the Academy by Dr. Sadleir, 

 the present Provost, and by our late lamented President, Provost 

 Lloyd, that ardent patron of learning and talent, to whose aflPec- 

 tionate and constant encouragement Mac Cullagh, in common with 

 many others who have since distinguished themselves in the Uni- 

 versity, owed much of his subsequent success. 



Previous to this, however, and whilst he was an undergraduate 

 in the University, he had completed a new and original theory of 

 the rotation of a solid body round a fixed point, of which he fur- 

 nished a brief sketch to Provost Lloyd ; this paper he did not pub- 

 lish, finding that he was anticipated in a portion of it by Poinsot, 

 as we shall hereafter have occasion to notice. 



The next subject to which he turned his attention was the Wave 

 Theory of Light, in which he afterwards became so eminent. At that 

 time the laws of Double Refraction had been discovered by Fresnel ; 

 but to explain those laws on mechanical principles, that author had 

 recourse to an hypothesis, simple, certainly, but so improbable as to 

 be now considered inadmissible ; from that hypothesis he succeeded 

 in deducing the laws at which he had previously arrived, but by a 

 process of calculation so complex, repulsive, and difiicult, as to be 

 almost unpresentable. It was on this subject that Professor Mac 

 Cullagh communicated to the Academy his first paper, read June 21 

 1830. Struck with the elegance of the laws, and with the simplicity 

 of the hypothesis by which they were explained, he was dissatisfied 

 with the difficulty of the process employed by Fresnel; and taking up 



