1913-14.] Obituary Notices. 281 
ten years ago, the Society showed its appreciation of the great service 
Dr Mackay rendered to scientific learning. His extensive knowledge of 
books was recognised by his appointment as a member of the Permanent 
International Bibliographical Association. His alma mater , the Univer- 
sity of St Andrews, readily granted him the highest distinction she could 
offer and in 1884 conferred on him the degree of LL.D. He served two 
periods as Examiner in Mathematics in St Andrews, and for many years 
he occupied a similar position on the Examining Board of the Chartered 
Accountants’ Society of Scotland. He was elected by the Edinburgh 
Mathematical Society as its first President, and it is not the least of his 
claims to our remembrance that he gave such whole-hearted support to 
its affairs that it was a constant pleasure to him to see it grow from a 
small beginning, with a membership of two score, to its present position of 
influence, with a membership of two hundred and fifty scattered over the 
four quarters of the globe. His zeal for the welfare of the Society never 
diminished, and until within the last few years, when his health began to 
decline, he was seldom absent from its meetings. As was to be expected 
from such an accomplished French scholar as he was, he took a very 
prominent part in the work of the Franco-Scottish Society, and attended 
several of its excursions through France. 
In giving an account of the scientific work of the late Dr Mackay, it 
will be simplest to deal with it in the historical order of its development. 
At the outset, it is no exaggeration to say that the whole domain of pure 
geometry, in so far as it deals with plane figures, came under his notice, and 
a list of his published papers will show that he enriched almost every part 
of the subject by discoveries of more or less importance. A very prominent 
place must be assigned to his knowledge of Greek geometry. His great 
command over Latin and Greek made him singularly well qualified to deal 
with this fascinating subject, and only a mere chapter of accidents prevented 
him from obtaining the full honour to which his labours entitled him. 
The seventeenth- and eighteenth-century geometers like Commandinus, 
Edmund Halley, and Robert Simson had studied and edited, as far as they 
could, the works of Archimedes, Apollonius, Euclid, and Diophantos, and 
fairly complete collections of the works of these mathematicians were 
available ; but very little attention had been paid to the writings of Pappus, 
one of the latest of the Alexandrian school of mathematicians. Dr Mackay 
made up his mind to supply the defect, and for many years he spent his 
vacations working patiently and laboriously at the MSS. of Pappus in the 
British Museum and in the Continental libraries, collating and translating 
them. He had practically finished his task, when Hultsch, the celebrated 
