PRESIDENTIAL ADDRESS. 



and chemistry. Born in 1832, and as a young man ap- 

 pointed assistant to Hofmann the chemist, his scientific 

 career extended over a period of seventy years. During 

 the whole of this long life his activity as a scientific inves- 

 tigator was extraordinary. The isolation of a new metal, 

 thallium, in 1861, early brought him fame. For twelve 

 years he investigated the properties of the new element, 

 finally determining the atomic mass with great accuracy. 

 To increase the precision of the results in this research, the 

 materials were weighed in a partial vacuum. Even then 

 the determinations showed slight irregularities. Following 

 up the residual discrepancies with painstaking persistence 

 like the genius he was, Crookes was rewarded by the dis- 

 covery of 'a repulsion resulting from radiation.' The ex- 

 planation of the novel phenomena in gases at low pressure 

 here disentangled by Orookes is associated with some fam- 

 ous names and is appreciated by few, but an exquisite piece 

 of apparatus invented by Orookes to show the repulsion, 

 known as the 'Orookes' radiometer' or 'light mill,' is so 

 common as to be seen on hawker's trays in Sydney. The 

 idea of investigating the electric discharge in gases perhaps 

 naturally presented itself at this time to Crookes, now 

 specially expert in the technique connected with experi- 

 ments at low pressure. A result of these wonderful 

 researches is the series of 'Crookes' tubes,' so well known 

 to every student of electricity, with which Orookes found 

 and demonstrated the properties of the cathode rays. Many 

 years later it was with one of these Orookes' tubes that 

 Rontgen made his sensational discovery. Crookes was, as 

 a chemist, equally famous. In 1857 he found the seleno- 

 cyanides. Following his discovery that under the bombard- 

 ment of the cathode rays a large number of substances emit 

 phosphorescent light, he elaborated anew method of spectro- 

 scopic analysis. In his hands the method has given valuable 

 results, the outcome of a very lengthy series of researches 



