APRIL 9, 1914| 
NATURE 
ee 
parts of a circuit were displayed, and their in- 
tricacies unravelled, for the first time; identity of 
energy might legitimately be urged as a supple- 
ment to conservation; and it is to these papers 
that we owe that fundamental generalisation, con- 
necting mechanical motion with electric and 
magnetic forces, which is known all over the world 
as ‘“ Poynting’s Theorem.” 
The work on radiation appeared partly in the | 
Phil. Trans. for 1904 and partly in the Phil. Mag. 
for 1905. In these memoirs the tangential pres- 
sure of radiation is analysed and demonstrated ; 
and it is shown, both theoretically and experi- 
mentally, that a beam of light behaves essentially 
as a stream of momentum, and gives all the 
mechanical results which may thus be expected, 
though of a magnitude exceedingly minute. 
Nevertheless, he goes,,on to show that these 
radiation-pressures, however small, are of much 
consequence in astronomy, and have many inter- 
esting and some conspicuous results. A  note- 
worthy part of his radiation memoirs, however, 
is independent of considerations of pressure or 
momentum, and gives a means of determining the 
absolute temperatures of sun and planets, and of 
space, in a singularly clear and_ conclusive 
manner. 
It is impossible, in a brief notice like this, to do 
justice to these great treatises, or to the rest of 
Poynting’s scientific work; it must suffice to inen- 
tion the titles of a few of his other papers :— 
“Change of State Solid-Liquid” (Phil. Mag., 
1881); ‘““A Double Image Micrometer” (Monthly 
MOUGCeS a) k.A.S., 1892); \ Osmotic Pressure ” 
(Phil. Mag., 1896); “On a Simple. Form of 
Saccharimeter ” (Proc. Phys. Soc., 1881). 
Among his publications is a series of text-books 
on physics, written in conjunction with his friend, 
Sir J. J. Thomson; but he has also produced 
smaller and more popular books, one on ‘The 
Pressure of Light” (S.P.C.K.), and one on ‘The 
Earth” (Camb. Univ. Press). He also took an 
interest in statistical science, and wrote on 
“Fluctuations in the Price of Wheat,” and on 
““Drunkenness Statistics of Large Towns.” 
His public spirit was shown by his accepting 
the position of a justice of the peace. 
He took some interest also in the philosophical 
aspects of physical science, and his help is acknow- 
ledged by Prof. James Ward in connection with 
the publication of a series of Gifford Lectures. 
Poynting was strongly inclined, almost unduly, 
to limit the province of science to description, and 
to regard a law of nature as nothing but a formu- 
lation of observed similarities. He wished to 
abolish the idea of cause in physics. In some of 
this he may have gone too far, but his rebellion 
against an excessive anthropomorphism which kad 
begun to cling around the notion of natural laws, 
as if they were really legal enactments to be 
obeyed or disobeyed by inert matter almost as if 
it possessed will-power and could exercise choice, 
some substances being praised as good radiators 
while others are stigmatised as bad—most gases 
being admittedly unable to reach a standard of 
NO. 2319, VOL. 93] 
perfection heid out to them as Boyle’s law, though 
a few of excessive merit might surpass it,— 
Poynting’s revolt against this kind of attitude to 
laws of nature, though doubtless more than half 
humorous, was in itself wholesome. His _philo- 
sophic views may be read, as a Presidential Ad- 
dress to Section A, in the Reports of the British 
Association for 1899. 
But I must not delay further on his scientific 
work; the man himself was even more than his 
work. When the Mason College became the 
University of Birmingham Poynting was elected 
Dean of the Faculty of Science; in that capacity 
his quiet wisdom and efficiency were very mani- 
fest, and keen was the regret of all his colleagues 
when, some twelve years later, failing health 
necessitated his yielding this office to another. 
His judgment was as sound as his knowledge, and 
his conspicuous fairness endeared him to colleagues 
and the members of his staff. By the latter it is 
not too much to say that he was regarded with 
affectionate veneration; one of them writes to me 
as follows :— 
“As to his character it is impossible to give 
the right impression to those who did not know 
him well. I consider him a man of very 
extraordinary ability, which might have carried 
him much farther if it had been associated with 
more self-assertion. But it was largely this 
modesty and self-suppression which created a very 
unusual degree of affection in those who had the 
privilege of knowing him intimately. I always 
associate him in my mind with Faraday and 
Stokes.” 
As a lecturer and teacher he was admirable, 
and the respect in which he was held by his peers 
was noteworthy. I am glad to remember that so 
recently as the last meeting of the British Asso- 
ciation, some of the greatest physicists in the 
world, who were staying with me—Prof. H. A. 
Lorentz, Lord Rayleigh, and Sir Joseph Larmor— 
went to his house one evening, and met there in 
his study Sir J. J. Thomson and Dr. Glazebrook, 
who were staying with him; thus constituting a 
remarkably representative gathering, and giving 
him a pleasure which he remembered to the end 
of his life. 
There is much more that might be said; but 
let his position in the world of science be what it 
may, we in the University of his mature life knew 
him well, and know him best as an admirable col- 
league, a staunch friend, and a good man. 
At the Memorial service, the following true 
words concerning him were spoken by the Rev. 
Henry Gow, who knew him well :— 
We remember that he did work to make him famous 
throughout the world of science which gave him a 
high place amongst the discoverers of truth; but we 
remember much more than that. We remember how 
he loved life, how interested he was in little things, 
how he delighted in children, in flowers, and in birds; 
what confidence and affection he inspired, how free 
he was from claims of self and from uneasy egotism ; 
how much happiness he felt and gave. We remember 
his wise judgments, strong character, cheerful 
courage, his delightful humour. and a certain peace- 
