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

be encountered. Difficulties

began at the very commencement of the process, and were

experienced in one form or another at every subsequent stage. In

the first place, the mere casting of a great disc of this mixture

of tin and copper, weighing something like three or four tons,

involved very troublesome problems. No doubt a casting of this

size, if the material had been, for example, iron, would

have offered no difficulties beyond those with which every

practical founder is well acquainted, and which he has to

encounter daily in the course of his ordinary work. But speculum

metal is a material of a very intractable description. There is,

of course, no practical difficulty in melting the copper, nor

in adding the proper proportion of tin when the copper has been

melted. There may be no great difficulty in arranging an

organization by which several crucibles, filled with the molten

material, shall be poured simultaneously so as to obtain the

requisite mass of metal, but from this point the difficulties

begin. For speculum metal when cold is excessively brittle, and

were the casting permitted to cool like an ordinary copper or iron

casting, the mirror would inevitably fly into pieces. Lord Rosse,

therefore, found it necessary to anneal the casting with extreme

care by allowing it to cool very slowly. This was accomplished by

drawing the disc of metal as soon as it had entered into the solid

state, though still glowing red, into an annealing oven. There

the temperature was allowed to subside so gradually, that six

weeks elapsed before the mirror had reached the temperature of the

external air. The necessity for extreme precaution in the

operation of annealing will be manifest if we reflect on one of

the accidents which happened. On a certain occasion, after the

cooling of a great casting had been completed, it was found, on

withdrawing the speculum, that it was cracked into two pieces.

This mishap was eventually traced to the fact that one of the

walls of the oven had only a single brick in its thickness, and

that therefore the heat had escaped more easily through that side

than through the other sides which were built of double thickness.

The speculum had, consequently, not cooled uniformly, and hence

the fracture had resulted. Undeterred, however, by this failure,

as well as by not a few other difficulties, into a description of

which we cannot now enter, Lord Rosse steadily adhered to his

self-imposed task, and at last succeeded in casting two perfect

discs on which to commence the tedious processes of grinding and

polishing. The magnitude of the operations involved may perhaps

be appreciated if I mention that the value of the mere copper and

tin entering into the composition of each of the mirrors was about

500 pounds.

 

In no part of his undertaking was Lord Rosse’s mechanical

ingenuity more taxed than in the devising of the mechanism for

carrying out the delicate operations of grinding and polishing the

mirrors, whose casting we have just mentioned. In the ordinary

operations of the telescope-maker, such processes had hitherto

been generally effected by hand, but, of course, such methods

became impossible when dealing with mirrors which were as large as

a good-sized dinner table, and whose weight was measured by

tons. The rough grinding was effected by means of a tool of cast

iron about the same size as the mirror, which was moved by

suitable machinery both backwards and forwards, and round and

round, plenty of sand and water being supplied between the mirror

and the tool to produce the necessary attrition. As the process

proceeded and as the surface became smooth, emery was used instead

of sand; and when this stage was complete, the grinding tool was

removed and the polishing tool was substituted. The essential

part of this was a surface of pitch, which, having been

temporarily softened by heat, was then placed on the mirror, and

accepted from the mirror the proper form. Rouge was then

introduced as the polishing powder, and the operation was

continued about nine hours, by which time the great mirror

had acquired the appearance of highly polished silver. When

completed, the disc of speculum metal was about six feet across

and four inches thick. The depression in the centre was about

half an inch. Mounted on a little truck, the great speculum was

then conveyed to the instrument, to be placed in its receptacle at

the bottom of the tube, the length of which was sixty feet, this

being the focal distance of the mirror. Another small reflector

was inserted in the great tube sideways, so as to direct the gaze

of the observer down upon the great reflector. Thus was completed

the most colossal instrument for the exploration of the heavens

which the art of man has ever constructed.

 

[PLATE: ROMAN CATHOLIC CHURCH AT PARSONSTOWN.]

 

It was once my privilege to be one of those to whom the

illustrious builder of the great telescope entrusted its use. For

two seasons in 1865 and 1866 I had the honour of being Lord

Rosse’s astronomer. During that time I passed many a fine night

in the observer’s gallery, examining different objects in the

heavens with the aid of this remarkable instrument. At the

time I was there, the objects principally studied were the

nebulae, those faint stains of light which lie on the background

of the sky. Lord Rosse’s telescope was specially suited for the

scrutiny of these objects, inasmuch as their delicacy required all

the light-grasping power which could be provided.

 

One of the greatest discoveries made by Lord Rosse, when his huge

instrument was first turned towards the heavens, consisted in the

detection of the spiral character of some of the nebulous forms.

When the extraordinary structure of these objects was first

announced, the discovery was received with some degree of

incredulity. Other astronomers looked at the same objects, and

when they failed to discern—and they frequently did fail to

discern—the spiral structure which Lord Rosse had indicated, they

drew the conclusion that this spiral structure did not exist.

They thought it must be due possibly to some instrumental defect

or to the imagination of the observer. It was, however, hardly

possible for any one who was both willing and competent to examine

into the evidence, to doubt the reality of Lord Rosse’s

discoveries. It happens, however, that they have been recently

placed beyond all doubt by testimony which it is impossible to

gainsay. A witness never influenced by imagination has now come

forward, and the infallible photographic plate has justified Lord

Rosse. Among the remarkable discoveries which Dr. Isaac Roberts

has recently made in the application of his photographic apparatus

to the heavens, there is none more striking than that which

declares, not only that the nebulae which Lord Rosse described as

spirals, actually do possess the character so indicated, but that

there are many others of the same description. He has even

brought to light the astonishingly interesting fact that there are

invisible objects of this class which have never been seen by

human eye, but whose spiral character is visible to the peculiar

delicacy of the photographic telescope.

 

In his earlier years, Lord Rosse himself used to be a diligent

observer of the heavenly bodies with the great telescope which was

completed in the year 1845. But I think that those who knew Lord

Rosse well, will agree that it was more the mechanical processes

incidental to the making of the telescope which engaged his

interest than the actual observations with the telescope when it

was completed. Indeed one who was well acquainted with him

believed Lord Rosse’s special interest in the great telescope

ceased when the last nail had been driven into it. But the

telescope was never allowed to lie idle, for Lord Rosse always had

associated with him some ardent young astronomer, whose delight it

was to employ to the uttermost the advantages of his position in

exploring the wonders of the sky. Among those who were in this

capacity in the early days of the great telescope, I may mention

my esteemed friend Dr. Johnston Stoney.

 

Such was the renown of Lord Rosse himself, brought about by his

consummate mechanical genius and his astronomical discoveries, and

such the interest which gathered around the marvellous workshops

at Birr castle, wherein his monumental exhibitions of optical

skill were constructed, that visitors thronged to see him from all

parts of the world. His home at Parsonstown became one of

the most remarkable scientific centres in Great Britain; thither

assembled from time to time all the leading men of science in the

country, as well as many illustrious foreigners. For many years

Lord Rosse filled with marked distinction the exalted position of

President of the Royal Society, and his advice and experience in

practical mechanical matters were always at the disposal of those

who sought his assistance. Personally and socially Lord

Rosse endeared himself to all with whom he came in contact. I

remember one of the attendants telling me that on one occasion he

had the misfortune to let fall and break one of the small mirrors

on which Lord Rosse had himself expended many hours of hard

personal labour. The only remark of his lordship was that

“accidents will happen.”

 

The latter years of his life Lord Rosse passed in comparative

seclusion; he occasionally went to London for a brief sojourn

during the season, and he occasionally went for a cruise in his

yacht; but the greater part of the year he spent at Birr Castle,

devoting himself largely to the study of political and social

questions, and rarely going outside the walls of his demesne,

except to church on Sunday mornings. He died on October 31, 1867.

 

He was succeeded by his eldest son, the present Earl of Rosse, who

has inherited his father’s scientific abilities, and done much

notable work with the great telescope.

 

AIRY.

 

In our sketch of the life of Flamsteed, we have referred to the

circumstances under which the famous Observatory that crowns

Greenwich Hill was founded. We have also had occasion to mention

that among the illustrious successors of Flamsteed both Halley and

Bradley are to be included. But a remarkable development of

Greenwich Observatory from the modest establishment of early days

took place under the direction of the distinguished astronomer

whose name is at the head of this chapter. By his labours this

temple of science was organised to such a degree of perfection

that it has served in many respects as a model for other

astronomical establishments in various parts of the world. An

excellent account of Airy’s career has been given by Professor H.

H. Turner, in the obituary notice published by the Royal

Astronomical Society. To this I am indebted for many of the

particulars here to be set down concerning the life of the

illustrious Astronomer Royal.

 

The family from which Airy took his origin came from Kentmere, in

Westmoreland. His father, William Airy, belonged to a

Lincolnshire branch of the same stock. His mother’s maiden name

was Ann Biddell, and her family resided at Playford, near Ipswich.

William Airy held some small government post which necessitated an

occasional change of residence to different parts of the country,

and thus it was that his son, George Biddell, came to be born at

Alnwick, on 27th July, 1801. The boy’s education, so far as

his school life was concerned was partly conducted at Hereford and

partly at Colchester. He does not, however, seem to have derived

much benefit from the hours which he passed in the schoolroom.

But it was delightful to him to spend his holidays on the farm at

Playford, where his uncle, Arthur Biddell, showed him much

kindness. The scenes of his early youth remained dear to Airy

throughout his life, and in subsequent years he himself owned a

house at Playford, to