Great Astronomers by Robert Stawell Ball (best ereader for students .txt) 📖

in life, as

we have already mentioned.

 

[PLATE: ASTRONOMETER MADE BY SIR J. HERSCHEL to compare the light

of certain stars by the intervention of the moon.]

 

The surroundings among which the young astronomer was reared

afforded him an excellent training for that career on which he was

to enter, and in which he was destined to attain a fame only less

brilliant than that of his father. The circumstances of his youth

permitted him to enjoy one great advantage which was denied to the

elder Herschel. He was able, from his childhood, to devote

himself almost exclusively to intellectual pursuits. William

Herschel, in the early part of his career, had only been able to

snatch occasional hours for study from his busy life as a

professional musician. But the son, having been born with

a taste for the student’s life, was fortunate enough to have been

endowed with the leisure and the means to enjoy it from the

commencement. His early years have been so well described by the

late Professor Pritchard in the “Report of the Council of the

Royal Astronomical Society for 1872,” that I venture to make an

extract here:—

 

“A few traits of John Herschel’s boyhood, mentioned

by himself in his maturer life, have been treasured up by those

who were dear to him, and the record of some of them may satisfy a

curiosity as pardonable as inevitable, which craves to learn

through what early steps great men or great nations become

illustrious. His home was singular, and singularly calculated to

nurture into greatness any child born as John Herschel was with

natural gifts, capable of wide development. At the head of the

house there was the aged, observant, reticent philosopher, and

rarely far away his devoted sister, Caroline Herschel, whose

labours and whose fame are still cognisable as a beneficent

satellite to the brighter light of her illustrious brother. It

was in the companionship of these remarkable persons, and under

the shadow of his father’s wonderful telescope, that John Herschel

passed his boyish years. He saw them, in silent but ceaseless

industry, busied about things which had no apparent concern with

the world outside the walls of that well-known house, but which,

at a later period of his life, he, with an unrivalled eloquence,

taught his countrymen to appreciate as foremost among those living

influences which but satisfy and elevate the noblest instincts of

our nature. What sort of intercourse passed between the father

and the boy may be gathered from an incident or two which he

narrated as having impressed themselves permanently on the memory

of his youth. He once asked his father what he thought was the

oldest of all things. The father replied, after the Socratic

method, by putting another question: ‘And what do you yourself

suppose is the oldest of all things?’ The boy was not successful

in his answers, thereon the old astronomer took up a small stone

from the garden walk: “There, my child, there is the oldest of all

the things that I certainly know.’ On another occasion his father

is said to have asked the boy, ‘What sort of things, do you think,

are most alike?’ The delicate, blue-eyed boy, after a short pause,

replied, ‘The leaves of the same tree are most like each other.’

‘Gather, then, a handful of leaves of that tree,’ rejoined the

philosopher, ‘and choose two that are alike.’ The boy failed; but

he hid the lesson in his heart, and his thoughts were revealed

after many days. These incidents may be trifles; nor should we

record them here had not John Herschel himself, though singularly

reticent about his personal emotions, recorded them as having made

a strong impression on his mind. Beyond all doubt we can trace

therein, first, that grasp and grouping of many things in one,

implied in the stone as the oldest of things; and, secondly, that

fine and subtle discrimination of each thing out of many like

things as forming the main features which characterized the habit

of our venerated friend’s philosophy.”

 

John Herschel entered St. John’s College, Cambridge, when he was

seventeen years of age. His university career abundantly

fulfilled his father’s eager desire, that his only son should

develop a capacity for the pursuit of science. After obtaining

many lesser distinctions, he finally came out as Senior Wrangler

in 1813. It was, indeed, a notable year in the mathematical

annals of the University. Second on that list, in which

Herschel’s name was first, appeared that of the illustrious

Peacock, afterwards Dean of Ely, who remained throughout life

one of Herschel’s most intimate friends.

 

Almost immediately after taking his degree, Herschel gave evidence

of possessing a special aptitude for original scientific

investigation. He sent to the Royal Society a mathematical paper

which was published in the PHILOSOPHICAL TRANSACTIONS. Doubtless

the splendour that attached to the name he bore assisted him in

procuring early recognition of his own great powers. Certain it

is that he was made a Fellow of the Royal Society at the

unprecedentedly early age of twenty-one. Even after this

remarkable encouragement to adopt a scientific career as the

business of his life, it does not seem that John Herschel at first

contemplated devoting himself exclusively to science. He

commenced to prepare for the profession of the Law by entering as

a student at the Middle Temple, and reading with a practising

barrister.

 

But a lawyer John Herschel was not destined to become.

Circumstances brought him into association with some leading

scientific men. He presently discovered that his inclinations

tended more and more in the direction of purely scientific

pursuits. Thus it came to pass that the original intention as to

the calling which he should follow was gradually abandoned.

Fortunately for science Herschel found its pursuit so attractive

that he was led, as his father had been before him, to give up his

whole life to the advancement of knowledge. Nor was it unnatural

that a Senior Wrangler, who had once tasted the delights of

mathematical research, should have been tempted to devote much

time to this fascinating pursuit. By the time John Herschel was

twenty-nine he had published so much mathematical work, and his

researches were considered to possess so much merit, that the

Royal Society awarded him the Copley Medal, which was the highest

distinction it was capable of conferring.

 

At the death of his father in 1822, John Herschel, with his tastes

already formed for a scientific career, found himself in the

possession of ample means. To him also passed all his father’s

great telescopes and apparatus. These material aids, together

with a dutiful sense of filial obligation, decided him to make

practical astronomy the main work of his life. He decided to

continue to its completion that great survey of the heavens which

had already been inaugurated, and, indeed, to a large extent

accomplished, by his father.

 

The first systematic piece of practical astronomical work which

John Herschel undertook was connected with the measurement of what

are known as “Double Stars.” It should be observed, that there

are in the heavens a number of instances in which two stars are

seen in very close association. In the case of those objects to

which the expression “Double Stars” is generally applied, the two

luminous points are so close together that even though they might

each be quite bright enough to be visible to the unaided eye, yet

their proximity is such that they cannot be distinguished as two

separate objects without optical aid. The two stars seem fused

together into one. In the telescope, however, the bodies may be

discerned separately, though they are frequently so close together

that it taxes the utmost power of the instrument to indicate the

division between them.

 

The appearance presented by a double star might arise from the

circumstance that the two stars, though really separated from each

other by prodigious distances, happened to lie nearly in the same

line of vision, as seen from our point of view. No doubt, many of

the so-called double stars could be accounted for on this

supposition. Indeed, in the early days when but few double stars

were known, and when telescopes were not powerful enough to

exhibit the numerous close doubles which have since been brought

to light, there seems to have been a tendency to regard all double

stars as merely such perspective effects. It was not at first

suggested that there could be any physical connection between the

components of each pair. The appearance presented was regarded as

merely due to the circumstance that the line joining the two

bodies happened to pass near the earth.

 

[PLATE: SIR JOHN HERSCHEL.]

 

In the early part of his career, Sir William Herschel seems to

have entertained the view then generally held by other astronomers

with regard to the nature of these stellar pairs. The great

observer thought that the double stars could therefore be made to

afford a means of solving that problem in which so many of the

observers of the skies had been engaged, namely, the determination

of the distances of the stars from the earth. Herschel saw that

the displacement of the earth in its annual movement round the sun

would produce an apparent shift in the place of the nearer of the

two stars relatively to the other, supposed to be much more

remote. If this shift could be measured, then the distance of the

nearer of the stars could be estimated with some degree of

precision.

 

As has not unfrequently happened in the history of science, an

effect was perceived of a very different nature from that which

had been anticipated. If the relative places of the two stars had

been apparently deranged merely in consequence of the motion of

the earth, then the phenomenon would be an annual one. After the

lapse of a year the two stars would have regained their original

relative positions. This was the effect for which William

Herschel was looking. In certain of the so called double stars,

he, no doubt, did find a movement. He detected the remarkable

fact that both the apparent distance and the relative positions of

the two bodies were changing. But what was his surprise to

observe that these alterations were not of an annually periodic

character. It became evident then that in some cases one of the

component stars was actually revolving around the other, in an

orbit which required many years for its completion. Here was

indeed a remarkable discovery. It was clearly impossible to

suppose that movements of this kind could be mere apparent

displacements, arising from the annual shift in our point of view,

in consequence of the revolution of the earth. Herschel’s

discovery established the interesting fact that, in certain of

these double stars, or binary stars, as these particular objects

are more expressively designated, there is an actual orbital

revolution of a character similar to that which the earth performs

around the sun. Thus it was demonstrated that in these particular

double stars the nearness of the two components was not merely

apparent. The objects must actually lie close together at a

distance which is small in comparison with the distance at which

either of them is separated from the earth. The fact that the

heavens contain pairs of twin suns in mutual revolution was thus

brought to light.

 

In consequence of this beautiful discovery, the attention of

astronomers was directed to the subject of double stars with a

degree of interest which these objects had never before excited.

It was therefore not unnatural that John Herschel should have been

attracted to this branch of astronomical work. Admiration for his

father’s discovery alone might have suggested that the son should

strive to develop this territory newly opened up to research. But

it also happened that the mathematical talents of the younger

Herschel inclined his inquiries in the same direction.