7O 
NATURE 
[May 25, 1871 

history of double stars, commencing with the father’s 
first discoveries, and terminating only with the decease of 
the son. 
Probably the busiest part, where all was busy, in the 
younger Herschel’s laborious life, was passed between the 
ime of his Cambridge degree in 1813 and the period 
when he quitted England in order to supplement the ex- 
ploration of the heavens inthe Southern regions, which 
“his father had so ably commenced, if not completed, in 
the North. Those who have access to the Transactions 
of the various British scientific societies, and to the 
learned journals of the day, between 1816 and 1833, will 
be sure to find at brief intervals some important com- 
munication of his, enlarging the boundaries of human 
knowledge, and bearing the stamp of natural genius, cul- 
tivated and developed by honest labour. His fertility in 
this respect is truly amazing. Partly in conjunction with 
Sir James South, he re-observed the nebule and double 
stars the existence and the cosmical significance of which 
had first been brought to light by his father: at the same 
time adding to the list some thousands of celestial objects 
which had escaped even his sagacious observation. Like 
his father also he constructed his telescope with his own 
hands ; an instrument which for many years remained a 
specimen, unique in its optical capacities and in the 
efficient simplicity of its mechanical arrangements. 
Latterly it has been surpassed among amateurs by Mr. 
Lassell and by Lord Rosse, and among artists by Mr. 
Grubb ; but it was the Herschels who pointed the way 
and encouraged their successors to stand upon the 
shoulders of those who preceded them. 
Nevertheless astronomy was very far from engrossing 
his whole attention ; we doubt whether it absorbed even 
the half of it, for those who knew him best knew that the 
bias of his mind was mainly directed towards chemistry 
and light, and their cognate branches of physical inquiry. 
In 1819, when philosophical chemistry in England was 
perhaps at its lowest ebb, he rediscovered, and for the first 
time ascertained, the leading properties of the hyposul- 
phite salts, the existence of which had, unknown to 
Herschel, been previously surmised, and only surmised, 
by Berthollet. In particular he noted the property of the 
hyposulphite of soda, whereby, as he says, “chloride of 
silver newly precipitated is dissolved in this salt almost as 
readily as sugar.” We mention this circumstance because 
it was owing to this property of the hyposulphite alone, 
that Daguerre twenty years after was enabled practically 
to realise the hopes of Davy and Wedgwood, that the 
photographic pictures which they had already obtained 
might one day be fixed and preserved, even when sub- 
mitted to the action of light. Thus, indirectly, John 
Herschel may, in a strong sense, be regarded as the 
father of photography ; and at subsequent periods perhaps 
no man has entered more fully and philosophically into 
the actinic relations of light. It was during this most 
active period of his philosophical life that, attracted by 
the marvellous discoveries of Fresnel in connection with 
the undulatory theory of light, and after having studied 
and mastered what others had done before him, he set 
his own original powers to the task, and soon added to 
our knowledge fresh facts which they, his masters, had 
themselves overlooked. He discovered, for instance, that 
the relative positions of the optic axes in certain biaxal 
crystals were functions of the index of refraction ; and he 
for the first time ascertained certain other actions of 
crystallised media on polarised light, which placed him at 
once among the first rank of experimental physicists of 
his day. The results of these studies he embodied in a 
most remarkable treatise on Light, published in the “ En- 
cyclopzedia Metropolitana,” which up to the present date 
may be advantageously consulted by the most accom- 
plished student in this branch of physical inquiry. In 
the same great work will be found other treatises of his, 
on Sound, on Heat, and on Physical Astronomy, all of 

them bearing the stamp of genius and industry, and each 
one of them containing some specific advance beyond 
the condition in which he had found the subject. 
In 1830 Dr. Lardner induced him to join in the compo- 
sition of what he designated as the “ Cabinet Cyclopzedia,” 
and to this Herschel contribute the two most celebrated 
volumes, viz., the “ Preliminary Discourse on the Study 
of Natural Philosophy,” and subsequently the volume 
on Astronomy. There were but few, if any, men of that 
day who could have contributed either. The first of 
them has probably formed the delight, the instruction, 
and the encouragement of every person who has since 
pursued or admired a scientific career. In dignity, 
purity, and pregnancy of language; in profundity of 
thought, in copiousness of apposite illustration, in a cer- 
tain indefinable sweetness of persuasion, it, even at this 
day, captivates every mind that applies itself to its peru- 
sal. Here and there indeed its author gives rein to cer- 
tain metaphysical speculations on Causes and Force, 
which are now found not exactly to square with the con- 
ceptions of later psychological writers. But on such 
questions as Causation and Force,a man whose mind, 
like John Herschel’s, had been for half a century steeped 
in the difficult philosophy which embraces and pursues 
them both, may surely be more safely trusted than other 
minds, however subtle, whose extent of opportunity and 
of practical exercise have necessarily been inferior to 
his. We entertain a strong conviction that when meta- 
physical science shall, “by taking thought,” have arrived 
at the first cubit of its stature, the deliberate conceptions 
of Herschel will be found to be in the main correct. A 
mind like his could have no sympathy with a philosophy 
which logically admits the thought, that, under some pos- 
sible state of things, two and two can be equivalent to 
five. Speculative, he was by nature constrained to be 
such, but the practical side of his disciplined intellect 
sufficed to adjust the balance, and to prevent him from 
going deliberately wrong in his philosophy. 
We now reluctantly but necessarily pass over much 
that is interesting and instructive in the career of the 
younger Herschel, and approach that crucial period of 
his life, when, accompanied by his wife and family, he 
left England for the Cape of Good Hope in 1834. To 
most of us John Herschel is known chiefly as the most 
eminent of modern philosophical astronomers ; but the 
pursuit of astronomy was not the voluntary choice nor 
the chief bias of his intellectual life, it was rather the re- 
collections and the impressions of the happy home of 
his youthful years, and reverence for the illustrious head 
of it, which determined him to complete what his father 
had commenced with such imperturbable diligence, and 
such wonderful success. He became a great astronomer, 
rather through filial piety than through the promptings of 
a natural taste. As in the case of many other great men, 
some of whom still survive among us, his life-long career 
was determined by uncontrollable circumstances, while the 
inborn aptitude has lainin another direction. But passing 
over such thoughts, suffice it to say that Herschel quitted 
England for a long sojourn at the Cape of Good Hope, in 
order to survey those portions of the sidereal heavens 
which were beyond the reach of his own and his father’s 
instruments. This he did, and wisely and generously did 
at his own personal expense ; for happily, the posses- 
sion of a moderate fortune enabled him to follow his own 
bent, and placed him beyond the necessity of the aid and 
the interference of a patron. How wisely, sedulously, and 
successfully his time was spent in this happiest of volun- 
tary exiles, may be gathered from the perusal of perhaps 
the most remarkable volume on philosophical astronomy 
that has yet appeared. 
The publication of this volume was, however, long 
delayed ; he therein unconsciously followed the advice of 
the Roman poet, ‘‘nonum prematur in annum,” inasmuch 
as it was not given to the world as a whole until the year 
