IN MEMORIAM : WILLIAM ACKROYD, F.I.C., F.C.S. 469 
sure to be the occasion of welcome papers and remarks at his 
sectional meetings, and his loss will not only be keenly felt by 
local scientific workers, but in a far wider circle. 
He took a keen interest in education, and combined marked 
capacity as a teacher with that warm personal interest in his 
students that made them regard him as their true friend. He 
took great pains in promoting the popularisation of science by 
lantern lectures and by attractive papers in magazines for the 
people. 
Mr. Ackroyd was an active member of the Halifax Scientific 
Society, and was its first Honorary Secretary. He was also 
an ardent Freemason. Latterly he took a lively interest in 
the problems of colour in various chemical substances, and the 
discovery of radium, with the revolutionary problems to which 
its explanation gave rise, had a rare fascination for him, and 
it was with researches on the nature of this interesting and rare 
metal that he was most engrossed at the time of his death. He 
was a strong opponent of the electron theory. 
When the Yorkshire Geological and Polytechnic Society 
commenced the work of exploring the underground waters of 
Malham, Mr. Ackroyd became a member of the Chemists' Com- 
mittee and took a prominent part in the preliminary discussions. 
The consideration of the chemical tests to be used and the methods 
to be adopted was of great importance, as the investigation 
was in tlie nature of pioneer work, and the previous futile attempts 
to solve the mystery of the sources of the Aire made the chemists 
doubly anxious to devise tests which, whilst being innocuous to 
the fish, could be used in sufficiently large quantities to be 
readily detected under conditions of considerable dilution, and 
each of which could be readily detected in the presence of the 
others. Their choice fell upon common salt, sulphate of am- 
monium, and fluorescein, and the results were eminently satis- 
factory and issued in a triumphant solution of the problems 
which were faced ; and the experience gained proved of immense 
value in the subsequent investigations in the more complicated 
area of Ingleborough. Those, however, who took part in these 
early investigations will never forget the anxious anticipations 
with which the tons of testing material were carted to the moors 
