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

fame belonging to this great achievement had to

be shared between Le Verrier and another astronomer, J. C. Adams,

of Cambridge. In our chapter on this great English mathematician

we shall describe the manner in which he was independently led to

the same discovery.

 

Directly the planetary nature of the newly-discovered body had

been established, the great observatories naturally included this

additional member of the solar system in their working lists, so

that day after day its place was carefully determined. When

sufficient time had elapsed the shape and position of the orbit of

the body became known. Of course, it need hardly be said that

observations applied to the planet itself must necessarily provide

a far more accurate method of determining the path which it

follows, than would be possible to Le Verrier, when all he had to

base his calculations upon was the influence of the planet

reflected, so to speak, from Uranus. It may be noted that the

true elements of the planet, when revealed by direct observation,

showed that there was a considerable discrepancy between the track

of the planet which Le Verrier had announced, and that which the

planet was actually found to pursue.

 

The name of the newly-discovered body had next to be considered.

As the older members of the system were already known by the same

names as great heathen divinities, it was obvious that some

similar source should be invoked for a suggestion as to a name for

the most recent planet. The fact that this body was so remote in

the depths of space, not unnaturally suggested the name “Neptune.”

Such is accordingly the accepted designation of that mighty globe

which revolves in the track that at present seems to trace out the

frontiers of our system.

 

Le Verrier attained so much fame by this discovery, that when,

in 1854, Arago’s place had to be filled at the head of the great

Paris Observatory, it was universally felt that the discoverer of

Neptune was the suitable man to assume the office which

corresponds in France to that of the Astronomer Royal in England.

It was true that the work of the astronomical mathematician had

hitherto been of an abstract character. His discoveries had been

made at his desk and not in the observatory, and he had no

practical acquaintance with the use of astronomical instruments.

However, he threw himself into the technical duties of the

observatory with vigour and determination. He endeavoured to

inspire the officers of the establishment with enthusiasm for that

systematic work which is so necessary for the accomplishment of

useful astronomical research. It must, however, be admitted that

Le Verrier was not gifted with those natural qualities which would

make him adapted for the successful administration of such an

establishment. Unfortunately disputes arose between the Director

and his staff. At last the difficulties of the situation became

so great that the only possible solution was to supersede Le

Verrier, and he was accordingly obliged to retire. He was

succeeded in his high office by another eminent mathematician, M.

Delaunay, only less distinguished than Le Verrier himself.

 

Relieved of his official duties, Le Verrier returned to the

mathematics he loved. In his non-official capacity he continued

to work with the greatest ardour at his researches on the

movements of the planets. After the death of M. Delaunay, who was

accidentally drowned in 1873, Le Verrier was restored to the

directorship of the observatory, and he continued to hold the

office until his death.

 

The nature of the researches to which the life of Le Verrier was

subsequently devoted are not such as admit of description in a

general sketch like this, where the language, and still less the

symbols, of mathematics could not be suitably introduced. It

may, however, be said in general that he was particularly engaged

with the study of the effects produced on the movements of the

planets by their mutual attractions. The importance of this work

to astronomy consists, to a considerable extent, in the fact that

by such calculations we are enabled to prepare tables by which the

places of the different heavenly bodies can be predicted for

our almanacs. To this task Le Verrier devoted himself, and the

amount of work he has accomplished would perhaps have been deemed

impossible had it not been actually done.

 

The superb success which had attended Le Verrier’s efforts to

explain the cause of the perturbations of Uranus, naturally led

this wonderful computer to look for a similar explanation of

certain other irregularities in planetary movements. To a large

extent he succeeded in showing how the movements of each of the

great planets could be satisfactorily accounted for by the

influence of the attractions of the other bodies of the same

class. One circumstance in connection with these investigations

is sufficiently noteworthy to require a few words here. Just as

at the opening of his career, Le Verrier had discovered that

Uranus, the outermost planet of the then known system, exhibited

the influence of an unknown external body, so now it appeared to

him that Mercury, the innermost body of our system, was also

subjected to some disturbances, which could not be satisfactorily

accounted for as consequences of any known agents of attraction.

The ellipse in which Mercury revolved was animated by a slow

movement, which caused it to revolve in its plane. It appeared to

Le Verrier that this displacement was incapable of explanation by

the action of any of the known bodies of our system. He was,

therefore, induced to try whether he could not determine from the

disturbances of Mercury the existence of some other planet, at

present unknown, which revolved inside the orbit of the known

planet. Theory seemed to indicate that the observed alteration in

the track of the planet could be thus accounted for. He naturally

desired to obtain telescopic confirmation which might verify the

existence of such a body in the same way as Dr. Galle verified the

existence of Neptune. If there were, indeed, an intramercurial

planet, then it must occasionally cross between the earth and

the sun, and might now and then be expected to be witnessed in

the actual act of transit. So confident did Le Verrier feel in

the existence of such a body that an observation of a dark

object in transit, by Lescarbault on 26th March, 1859, was

believed by the mathematician to be the object which his theory

indicated. Le Verrier also thought it likely that another transit

of the same object would be seen in March, 1877. Nothing of the

kind was, however, witnessed, notwithstanding that an assiduous

watch was kept, and the explanation of the change in Mercury’s

orbit must, therefore, be regarded as still to be sought for.

 

Le Verrier naturally received every honour that could be

bestowed upon a man of science. The latter part of his life was

passed during the most troubled period of modern French history.

He was a supporter of the Imperial Dynasty, and during the

Commune he experienced much anxiety; indeed, at one time grave

fears were entertained for his personal safety.

 

Early in 1877 his health, which had been gradually failing for

some years, began to give way. He appeared to rally somewhat in

the summer, but in September he sank rapidly, and died on

Sunday, the 23rd of that month.

 

His remains were borne to the cemetery on Mont Parnasse in a

public funeral. Among his pallbearers were leading men of

science, from other countries as well as France, and the

memorial discourses pronounced at the grave expressed their

admiration of his talents and of the greatness of the services he

had rendered to science.

 

ADAMS.

 

The illustrious mathematician who, among Englishmen, at all

events, was second only to Newton by his discoveries in

theoretical astronomy, was born on June the 5th, 1819, at the

farmhouse of Lidcot, seven miles from Launceston, in Cornwall.

His early education was imparted under the guidance of the Rev.

John Couch Grylls, a first cousin of his mother. He appears to

have received an education of the ordinary school type in classics

and mathematics, but his leisure hours were largely devoted to

studying what astronomical books he could find in the library of

the Mechanics’ Institute at Devonport. He was twenty years old

when he entered St. John’s College, Cambridge. His career in the

University was one of almost unparalleled distinction, and it is

recorded that his answering at the Wranglership examination, where

he came out at the head of the list in 1843, was so high that he

received more than double the marks awarded to the Second

Wrangler.

 

Among the papers found after his death was the following

memorandum, dated July the 3rd, 1841: “Formed a design at the

beginning of this week of investigating, as soon as possible after

taking my degree, the irregularities in the motion of Uranus,

Which are as yet unaccounted for, in order to find whether they

may be attributed to the action of an undiscovered planet beyond

it; and, if possible, thence to determine the elements of its

orbit approximately, which would lead probably to its discovery.”

 

After he had taken his degree, and had thus obtained a little

relaxation from the lines within which his studies had

previously been necessarily confined, Adams devoted himself to

the study of the perturbations of Uranus, in accordance with the

resolve which we have just seen that he formed while he was

still an undergraduate. As a first attempt he made the

supposition that there might be a planet exterior to Uranus, at

a distance which was double that of Uranus from the sun. Having

completed his calculation as to the effect which such a

hypothetical planet might exercise upon the movement of Uranus,

he came to the conclusion that it would be quite possible to

account completely for the unexplained difficulties by the

action of an exterior planet, if only that planet were of

adequate size and had its orbit properly placed. It was

necessary, however, to follow up the problem more precisely,

and accordingly an application was made through Professor

Challis, the Director of the Cambridge Observatory, to the

Astronomer Royal, with the object of obtaining from the

observations made at Greenwich Observatory more accurate values

for the disturbances suffered by Uranus. Basing his work on the

more precise materials thus available, Adams undertook his

calculations anew, and at last, with his completed results, he

called at Greenwich Observatory on October the 21st, 1845. He

there left for the Astronomer Royal a paper which contained the

results at which he had arrived for the mass and the mean distance

of the hypothetical planet as well as the other elements necessary

for calculating its exact position.

 

[PLATE: JOHN COUCH ADAMS.]

 

As we have seen in the preceding chapter, Le Verrier had been also

investigating the same problem. The place which Le Verrier

assigned to the hypothetical disturbing planet for the beginning

of the year 1847, was within a degree of that to which Adams’s

computations pointed, and which he had communicated to the

Astronomer Royal seven months before Le Verrier’s work appeared.

On July the 29th, 1846, Professor Challis commenced to search for

the unknown object with the Northumberland telescope belonging to

the Cambridge Observatory. He confined his attention to a limited

region in the heavens, extending around that point to which Mr.

Adams’ calculations pointed. The relative places of all the

stars, or rather star-like objects within this area, were to be

carefully measured. When the same observations were repeated a

week or two later, then the distances of the several pairs of

stars from each other would be found unaltered, but any planet

which happened to lie among the objects measured would disclose

its existence by the alterations in distance due to its motion in

the interval. This method of search, though