6 . REPORT—1 890. 
Priestley the Copley Medal for a remarkable paper entitled ‘ Observations 
on Different Kinds of Air,’ and in that year he became librarian and 
literary companion to the Karl of Shelbourne (afterwards Marquis of 
Lansdowne), and thereby secured special advantages in the pursuit of 
his scientific researches. 
With respect to his departure from Leeds, he expressed himself as 
having been very happy there ‘ with a liberal, friendly, and harmonious 
congregation, to whom my services (of which I was not sparing) were 
very acceptable. Here I had no unreasonable prejudices to contend with, 
so that I had full scope for every kind of exertion; and I can truly say 
that I always considered the office of a Christian minister as the most 
honourable of any upon earth, and in the studies proper to it I always 
took the greatest pleasure.’ During the next five years he published as 
many volumes describing the results of important experiments on air. 
After investigating the properties of nitric oxide, and applying it to the 
analysis of air, Priestley, in 1774, discovered and carefully studied oxy- 
gen, which he obtained by the action of heat upon the red oxide of mer- 
cury. He was the first to prepare and study sulphurous acid, carbonic 
oxide, nitrous oxide, hydrochloric acid (marine acid air), and the fluoride 
of silicon, and carried out important researches on the properties of hydro- 
gen, and of other gases previously but little known. His great quickness 
of perception and power of experiment led him to the achievement of 
many novel and important results. But one cannot help contrasting his 
somewhat random search after new discoveries with the close logical 
reasoning and philosophic spirit which guided and pervaded the remark- 
able researches of him whose departure from amongst us since the last 
gathering of this Association is so universally deplored—of the great dis- 
coverer of the universal law of the conservation of energy, James Prescott 
Joule. I could not add to the judicious and graceful reference to his work 
which Sir Henry Roscoe was privileged to make, in the last year of that 
philosopher’s valuable life, when presiding over the recent meeting of 
the Association in the town which gloried in numbering Joule among its 
citizens; but I may, perhaps, be permitted to express the sanguine hope 
that the desire of the scientific world to secure the establishment of an 
international memorial fitly commemorative of his great life-work may be 
realised in the most ample manner. 
The wide scope of the admirable discourse delivered by Owen in this 
town thirty-two years ago affords an interesting illustration of the delight 
which men whose best energies are devoted to the cultivation of one 
particular branch of science take in the results of the labours of their 
fellow-workers in other departments, and in their achievements in con- 
tributing to the general advancement of our knowledge of Nature’s laws 
and of their operations. It is to this bond of intimate union between 
all workers in pure science that we owe the instructive reviews of the 
