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

study in his

beautiful home at Collingwood, in Kent.

 

His health having gradually failed, he died on the 11th May,

1871, in the seventy-ninth year of his age.

 

THE EARL OF ROSSE.

 

The subject of our present sketch occupies quite a distinct

position in scientific history. Unlike many others who have risen

by their scientific discoveries from obscurity to fame, the great

Earl of Rosse was himself born in the purple. His father, who,

under the title of Sir Lawrence Parsons, had occupied a

distinguished position in the Irish Parliament, succeeded on the

death of his father to the Earldom which had been recently

created. The subject of our present memoir was, therefore, the

third of the Earls of Rosse, and he was born in York on June

17, 1800. Prior to his father’s death in 1841, he was known as

Lord Oxmantown.

 

The University education of the illustrious astronomer was begun

in Dublin and completed at Oxford. We do not hear in his case of

any very remarkable University career. Lord Rosse was, however, a

diligent student, and obtained a first-class in mathematics. He

always took a great deal of interest in social questions, and was

a profound student of political economy. He had a seat in the

House of Commons, as member for King’s County, from 1821 to

1834, his ancestral estate being situated in this part of

Ireland.

 

[PLATE: THE EARL OF ROSSE.]

 

Lord Rosse was endowed by nature with a special taste for

mechanical pursuits. Not only had he the qualifications of a

scientific engineer, but he had the manual dexterity which

qualified him personally to carry out many practical arts. Lord

Rosse was, in fact, a skilful mechanic, an experienced founder,

and an ingenious optician. His acquaintances were largely among

those who were interested in mechanical pursuits, and it was his

delight to visit the works or engineering establishments where

refined processes in the arts were being carried on. It has often

been stated—and as I have been told by members of his family,

truly stated—that on one occasion, after he had been shown over

some large works in the north of England, the proprietor bluntly

said that he was greatly in want of a foreman, and would indeed be

pleased if his visitor, who had evinced such extraordinary

capacity for mechanical operations, would accept the post. Lord

Rosse produced his card, and gently explained that he was not

exactly the right man, but he appreciated the compliment, and this

led to a pleasant dinner, and was the basis of a long friendship.

 

I remember on one occasion hearing Lord Rosse explain how it was

that he came to devote his attention to astronomy. It appears

that when he found himself in the possession of leisure and of

means, he deliberately cast around to think how that means and

that leisure could be most usefully employed. Nor was it

surprising that he should search for a direction which would offer

special scope for his mechanical tastes. He came to the

conclusion that the building of great telescopes was an art which

had received no substantial advance since the great days of

William Herschel. He saw that to construct mighty instruments for

studying the heavens required at once the command of time and the

command of wealth, while he also felt that this was a subject the

inherent difficulties of which would tax to the uttermost whatever

mechanical skill he might possess. Thus it was he decided that

the construction of great telescopes should become the business of

his life.

 

[PLATE: BIRR CASTLE.

 

PLATE: THE MALL, PARSONSTOWN.]

 

In the centre of Ireland, seventy miles from Dublin, on the border

between King’s County and Tipperary, is a little town whereof we

must be cautious before writing the name. The inhabitants of that

town frequently insist that its name is Birr,* while the official

designation is Parsonstown, and to this day for every six people

who apply one name to the town, there will be half a dozen who use

the other. But whichever it may be, Birr or Parsonstown—and I

shall generally call it by the latter name—it is a favourable

specimen of an Irish county town. The widest street is called the

Oxmantown Mall. It is bordered by the dwelling-houses of the

chief residents, and adorned with rows of stately trees. At one

end of this distinctly good feature in the town is the Parish

Church, while at the opposite end are the gates leading into Birr

Castle, the ancestral home of the house of Parsons. Passing

through the gates the visitor enters a spacious demesne,

possessing much beauty of wood and water, one of the most pleasing

features being the junction of the two rivers, which unite at a

spot ornamented by beautiful timber. At various points

illustrations of the engineering skill of the great Earl will be

observed. The beauty of the park has been greatly enhanced by the

construction of an ample lake, designed with the consummate art by

which art is concealed. Even in mid-summer it is enlivened by

troops of wild ducks preening themselves in that confidence which

they enjoy in those happy localities where the sound of a gun is

seldom heard. The water is led into the lake by a tube which

passes under one of the two rivers just mentioned, while the

overflow from the lake turns a water-wheel, which works a pair of

elevators ingeniously constructed for draining the lowlying parts

of the estate.

 

*Considering the fame acquired by Parsonstown from Lord Rosse’s

mirrors, it may be interesting to note the following extract from

“The Natural History of Ireland,” by Dr. Gerard Boate, Thomas

Molyneux M.D., F.R.S., and others, which shows that 150 years ago

Parsonstown was famous for its glass:—

 

“We shall conclude this chapter with the glass, there having been

several glasshouses set up by the English in Ireland, none in

Dublin or other cities, but all of them in the country; amongst

which the principal was that of Birre, a market town, otherwise

called Parsonstown, after one Sir Lawrence Parsons, who, having

purchased that lordship, built a goodly house upon it; his son

William Parsons having succeeded him in the possession of it;

which town is situate in Queen’s County, about fifty miles

(Irish) to the southwest of Dublin, upon the borders of the two

provinces of Leinster and Munster; from this place Dublin was

furnished with all sorts of window and drinking glasses, and such

other as commonly are in use. One part of the materials, viz.,

the sand, they had out of England; the other, to wit the ashes,

they made in the place of ash-tree, and used no other. The

chiefest difficulty was to get the clay for the pots to melt the

materials in; this they had out of the north.”—Chap. XXI., Sect.

VIII. “Of the Glass made in Ireland.”

 

Birr Castle itself is a noble mansion with reminiscences from the

time of Cromwell. It is surrounded by a moat and a drawbridge of

modern construction, and from its windows beautiful views can be

had over the varied features of the park. But while the visitors

to Parsonstown will look with great interest on this residence of

an Irish landlord, whose delight it was to dwell in his own

country, and among his own people, yet the feature which they have

specially come to observe is not to be found in the castle itself.

On an extensive lawn, sweeping down from the moat towards the

lake, stand two noble masonry walls. They are turreted and clad

with ivy, and considerably loftier than any ordinary house. As

the visitor approaches, he will see between those walls what may

at first sight appear to him to be the funnel of a steamer lying

down horizontally. On closer approach he will find that it is an

immense wooden tube, sixty feet long, and upwards of six feet in

diameter. It is in fact large enough to admit of a tall man

entering into it and walking erect right through from one end to

the other. This is indeed the most gigantic instrument which has

ever been constructed for the purpose of exploring the heavens.

Closely adjoining the walls between which the great tube swings,

is a little building called “The Observatory.” In this the

smaller instruments are contained, and there are kept the books

which are necessary for reference. The observatory also offers

shelter to the observers, and provides the bright fire and the cup

of warm tea, which are so acceptable in the occasional intervals

of a night’s observation passed on the top of the walls with no

canopy but the winter sky.

 

Almost the first point which would strike the visitor to Lord

Rosse’s telescope is that the instrument at which he is looking is

not only enormously greater than anything of the kind that he has

ever seen before, but also that it is something of a totally

different nature. In an ordinary telescope he is accustomed to

find a tube with lenses of glass at either end, while the large

telescopes that we see in our observatories are also in general

constructed on the same principle. At one end there is the

object-glass, and at the other end the eye-piece, and of course it

is obvious that with an instrument of this construction it is to

the lower end of the tube that the eye of the observer must be

placed when the telescope is pointed to the skies. But in Lord

Rosse’s telescope you would look in vain for these glasses, and it

is not at the lower end of the instrument that you are to take

your station when you are going to make your observations. The

astronomer at Parsonstown has rather to avail himself of the

ingenious system of staircases and galleries, by which he

is enabled to obtain access to the mouth of the great tube. The

colossal telescope which swings between the great walls, like

Herschel’s great telescope already mentioned, is a reflector, the

original invention of which is due of course to Newton. The

optical work which is accomplished by the lenses in the ordinary

telescope is effected in the type of instrument constructed by

Lord Rosse by a reflecting mirror which is placed at the lower end

of the vast tube. The mirror in this instrument is made

of a metal consisting of two parts of copper to one of tin. As we

have already seen, this mixture forms an alloy of a very peculiar

nature. The copper and the tin both surrender their distinctive

qualities, and unite to form a material of a very different

physical character. The copper is tough and brown, the tin is no

doubt silvery in hue, but soft and almost fibrous in texture.

When the two metals are mixed together in the proportions I have

stated, the alloy obtained is intensely hard and quite brittle

being in both these respects utterly unlike either of the two

ingredients of which it is composed. It does, however, resemble

the tin in its whiteness, but it acquires a lustre far brighter

than tin; in fact, this alloy hardly falls short of silver itself

in its brilliance when polished.

 

[PLATE: LORD ROSSE’S TELESCOPE.

From a photograph by W. Lawrence, Upper Sackville Street, Dublin.]

 

The first duty that Lord Rosse had to undertake was the

construction of this tremendous mirror, six feet across, and about

four or five inches thick. The dimensions were far in excess of

those which had been contemplated in any previous attempt of the

same kind. Herschel had no doubt fashioned one mirror of four

feet in diameter, and many others of smaller dimensions, but the

processes which he employed had never been fully published, and it

was obvious that, with a large increase in dimensions,

great additional difficulties had to