章节正文
cannot imagine motion without some Power moving through the
medium of some subordinateagency, ever acting on the sun, to
send such floods of light and heat to our otherwise cold and dark
terrestrial ball; but it is the overwhelmingmagnitude of such
power that we are incapable of comprehending. The agency
necessary to throw out the floods of flame seen during the few
moments of a total eclipse of the sun, and the power requisite to
burst open a cavity in its surface, such as could entirely
engulph our earth, will ever set all the thinking capacity of man
at nought."
[4] The Observatory, Nos. 34, 42, 45, 49, and 58.
[5] We regret to say that Sheriff Barclay died a few months ago,
greatly respected by all who knew him.
[6] Sir E. Denison Beckett, in his Rudimentary Treatise on clocks
and Watches and Bells, has given an instance or the
telescope-driving clock, invented by Mr. Cooke (p. 213).
[7] J. Norman Lockyer, F.R.S.--Stargazing, Past and Present, p.
302.
[8] This excellent instrument is now in the possession of my
son-in-law, Dr. Hartree, of Leigh, near Tunbridge.
[9] An interesting account of Mr. Alvan Clark is given in
Professor Newcomb's 'Popular Astronomy,' p. 137.
[10] A photographicrepresentation of this remarkabletelescope
is given as the frontispiece to Mr. Lockyer's Stargazing, Past
and Present; and a full description of the instrument is given in
the text of the same work. This refractingtelescope did not
long remain the largest. Mr. Alvan Clark was commissioned to
erect a larger equatorial for Washington Observatory; the
object-glass (the rough disks of which were also furnished by
Messrs. Chance of Birmingham) exceeding in aperture that of Mr.
Cooke's by only one inch. This was finished and mounted in
November, 1873. Another instrument of similar size and power was
manufactured by Mr. Clark for the University of Virginia. But
these instruments did not long maintain their supremacy. In
1881, Mr. Howard Grubb, of Dublin, manufactured a still larger
instrument for the Austrian Government--the object-glass being of
twenty-seven inches aperture. But Mr. Alvan Clark was not to be
beaten. In 1882, he supplied the Russian Government with the
largest refractingtelescope in existence the object-glass being
of thirty inches diameter. Even this, however, is to be
surpassed by the lens which Mr. Clark has in hand for the Lick
Observatory (California), which is to have a clear aperture of
three feet in diameter.
[11] Since the above passage was written and in type, I have seen
(in September 1884) the reflecting telescope referred to at pp.
357-8. It was mounted on its cast-iron equatorial stand, and at
work in the field adjoining the village green at Bainbridge,
Yorkshire. The mirror of the telescope is 8 inches in diameter;
its focal length, 5 feet; and the tube in which it is mounted,
about 6 feet long. The instrument seemed to me to have an
excellent defining power.
But Mr. Lancaster, like every eager astronomer, is anxious for
further improvements. He considers the achromatic telescope the
king of instruments, and is now engaged in testing convex optical
surfaces, with a view to achieving a telescope of that
description. The chief difficulty is the heavy charge for the
circular blocks of flint glass requisite for the work which he
meditates. "That," he says, "is the great difficulty with
amateurs of my class." He has, however, already contrived and
constructed a machine for grinding and polishing the lenses in an
accurate convex form, and it works quite satisfactorily. Mr.
Lancaster makes his own tools. From the raw material, whether of
glass or steel, he produces the work required. As to tools, all
that he requires is a bar of steel and fire; his fertile brain
and busy hands do the rest. I looked into the little workshop
behind his sitting-room, and found it full of ingenious
adaptations. The turning lathe occupies a considerable part of
it; but when he requires more space, the village smith with his
stithy, and the miller with his water-power, are always ready to
help him. His tools, though not showy, are effective. His best
lenses are made by himself: those which he buys are not to be
depended upon. The best flint glass is obtained from Paris in
blocks, which he divides, grinds, and polishes to perfect form.
I was attracted by a newly made machine, placed on a table in the
sitting-room; and on inquiry found that its object was to grind
and polish lenses. Mr. Lancaster explained that the difficulty
to be overcome in a good machine, is to make the emery cut the
surface equally from centre to edge of the lens, so that the lens
will neither lengthen nor shorten the curve during its
production. To quote his words: "This really involves the
problem of the 'three bodies,' or disturbing forces so celebrated
in dynamical mathematics, and it is further complicated by
another quantity, the 'coefficient of attrition,' or work done by
the grinding material, as well as the mischief done by capillary
attractionand nodal points of superimposed curves in the path of
the tool. These complications tend to cause rings or waves of
unequal wear in the surface of the glass, and ruin the defining
power of the lens, which depends upon the uniformity of its
curve. As the outcome of much practical experiment, combined
with mathematicalresearch, I settled upon the ratio of speed
between the sheave of the lens-tool guide and the turn-table;
between whose limits the practical equalization of wear (or cut
of the emery) might with the greater facility be adjusted, by
means of varying the stroke and eccentricity of the tool. As the
result of these considerations in the construction of the
machine, the surface of the glass 'comes up' regularly all over
the lens; and the polishing only takes a few minutes' work--thus
keeping the truth of surface gained by using a rigid tool."
The machine in question consists of a revolving sheave or ring,
with a sliding strip across its diameter; the said strip having a
slot and clamping screw at one end, and a hole towards the other,
through which passes the axis of the tool used in forming the
lens,--the slot in the strip allowing the tool to give any stroke
from 0 to 1.25 inch. The lens is carried on a revolving
turn-table, with an arrangement to allow the axis of the lens to
coincide with the axis of the table. The ratio of speed between
the sheave and turn-table is arranged by belt and properly sized
pulleys, and the whole can be driven either by hand or by power.
The sheave merely serves as a guide to the tool in its path, and
the lens may either be worked on the turn-table or upon a chuck
attached to the tool rod. The work upon the lens is thus to a
great extent independent of the error of the machine through
shaking, or bad fitting, or wear; and the only part of the
machine which requires really first-class work is the axis of the
turn-table, which (in this machine) is a conical bearing at top,
with steel centre below,--the bearing turned, hardened, and then
ground up true, and run in anti-friction metal. Other details
might be given, but these are probably enough for present
purposes. We hope, at some future time, for a special detail of
Mr. Lancaster's interesting investigations, from his own mind and
pen.
[12] The translations are made by W. Cadwalladr Davies, Esq.
[13] This evidence was given by Mr. W. Cadwalladr Davies on the
28th October, 1880.
End
medium of some subordinateagency, ever acting on the sun, to
send such floods of light and heat to our otherwise cold and dark
terrestrial ball; but it is the overwhelmingmagnitude of such
power that we are incapable of comprehending. The agency
necessary to throw out the floods of flame seen during the few
moments of a total eclipse of the sun, and the power requisite to
burst open a cavity in its surface, such as could entirely
engulph our earth, will ever set all the thinking capacity of man
at nought."
[4] The Observatory, Nos. 34, 42, 45, 49, and 58.
[5] We regret to say that Sheriff Barclay died a few months ago,
greatly respected by all who knew him.
[6] Sir E. Denison Beckett, in his Rudimentary Treatise on clocks
and Watches and Bells, has given an instance or the
telescope-driving clock, invented by Mr. Cooke (p. 213).
[7] J. Norman Lockyer, F.R.S.--Stargazing, Past and Present, p.
302.
[8] This excellent instrument is now in the possession of my
son-in-law, Dr. Hartree, of Leigh, near Tunbridge.
[9] An interesting account of Mr. Alvan Clark is given in
Professor Newcomb's 'Popular Astronomy,' p. 137.
[10] A photographicrepresentation of this remarkabletelescope
is given as the frontispiece to Mr. Lockyer's Stargazing, Past
and Present; and a full description of the instrument is given in
the text of the same work. This refractingtelescope did not
long remain the largest. Mr. Alvan Clark was commissioned to
erect a larger equatorial for Washington Observatory; the
object-glass (the rough disks of which were also furnished by
Messrs. Chance of Birmingham) exceeding in aperture that of Mr.
Cooke's by only one inch. This was finished and mounted in
November, 1873. Another instrument of similar size and power was
manufactured by Mr. Clark for the University of Virginia. But
these instruments did not long maintain their supremacy. In
1881, Mr. Howard Grubb, of Dublin, manufactured a still larger
instrument for the Austrian Government--the object-glass being of
twenty-seven inches aperture. But Mr. Alvan Clark was not to be
beaten. In 1882, he supplied the Russian Government with the
largest refractingtelescope in existence the object-glass being
of thirty inches diameter. Even this, however, is to be
surpassed by the lens which Mr. Clark has in hand for the Lick
Observatory (California), which is to have a clear aperture of
three feet in diameter.
[11] Since the above passage was written and in type, I have seen
(in September 1884) the reflecting telescope referred to at pp.
357-8. It was mounted on its cast-iron equatorial stand, and at
work in the field adjoining the village green at Bainbridge,
Yorkshire. The mirror of the telescope is 8 inches in diameter;
its focal length, 5 feet; and the tube in which it is mounted,
about 6 feet long. The instrument seemed to me to have an
excellent defining power.
But Mr. Lancaster, like every eager astronomer, is anxious for
further improvements. He considers the achromatic telescope the
king of instruments, and is now engaged in testing convex optical
surfaces, with a view to achieving a telescope of that
description. The chief difficulty is the heavy charge for the
circular blocks of flint glass requisite for the work which he
meditates. "That," he says, "is the great difficulty with
amateurs of my class." He has, however, already contrived and
constructed a machine for grinding and polishing the lenses in an
accurate convex form, and it works quite satisfactorily. Mr.
Lancaster makes his own tools. From the raw material, whether of
glass or steel, he produces the work required. As to tools, all
that he requires is a bar of steel and fire; his fertile brain
and busy hands do the rest. I looked into the little workshop
behind his sitting-room, and found it full of ingenious
adaptations. The turning lathe occupies a considerable part of
it; but when he requires more space, the village smith with his
stithy, and the miller with his water-power, are always ready to
help him. His tools, though not showy, are effective. His best
lenses are made by himself: those which he buys are not to be
depended upon. The best flint glass is obtained from Paris in
blocks, which he divides, grinds, and polishes to perfect form.
I was attracted by a newly made machine, placed on a table in the
sitting-room; and on inquiry found that its object was to grind
and polish lenses. Mr. Lancaster explained that the difficulty
to be overcome in a good machine, is to make the emery cut the
surface equally from centre to edge of the lens, so that the lens
will neither lengthen nor shorten the curve during its
production. To quote his words: "This really involves the
problem of the 'three bodies,' or disturbing forces so celebrated
in dynamical mathematics, and it is further complicated by
another quantity, the 'coefficient of attrition,' or work done by
the grinding material, as well as the mischief done by capillary
attractionand nodal points of superimposed curves in the path of
the tool. These complications tend to cause rings or waves of
unequal wear in the surface of the glass, and ruin the defining
power of the lens, which depends upon the uniformity of its
curve. As the outcome of much practical experiment, combined
with mathematicalresearch, I settled upon the ratio of speed
between the sheave of the lens-tool guide and the turn-table;
between whose limits the practical equalization of wear (or cut
of the emery) might with the greater facility be adjusted, by
means of varying the stroke and eccentricity of the tool. As the
result of these considerations in the construction of the
machine, the surface of the glass 'comes up' regularly all over
the lens; and the polishing only takes a few minutes' work--thus
keeping the truth of surface gained by using a rigid tool."
The machine in question consists of a revolving sheave or ring,
with a sliding strip across its diameter; the said strip having a
slot and clamping screw at one end, and a hole towards the other,
through which passes the axis of the tool used in forming the
lens,--the slot in the strip allowing the tool to give any stroke
from 0 to 1.25 inch. The lens is carried on a revolving
turn-table, with an arrangement to allow the axis of the lens to
coincide with the axis of the table. The ratio of speed between
the sheave and turn-table is arranged by belt and properly sized
pulleys, and the whole can be driven either by hand or by power.
The sheave merely serves as a guide to the tool in its path, and
the lens may either be worked on the turn-table or upon a chuck
attached to the tool rod. The work upon the lens is thus to a
great extent independent of the error of the machine through
shaking, or bad fitting, or wear; and the only part of the
machine which requires really first-class work is the axis of the
turn-table, which (in this machine) is a conical bearing at top,
with steel centre below,--the bearing turned, hardened, and then
ground up true, and run in anti-friction metal. Other details
might be given, but these are probably enough for present
purposes. We hope, at some future time, for a special detail of
Mr. Lancaster's interesting investigations, from his own mind and
pen.
[12] The translations are made by W. Cadwalladr Davies, Esq.
[13] This evidence was given by Mr. W. Cadwalladr Davies on the
28th October, 1880.
End
- agency [´eidʒənsi]
n.代理商；机构；代理 (初中英语单词) - acting [´æktiŋ] a.代理的 n.演戏 (初中英语单词)
- otherwise [´ʌðəwaiz] ad.另外 conj.否则 (初中英语单词)
- capacity [kə´pæsiti] n.容量；智能；能力 (初中英语单词)
- sheriff [´ʃerif] n.郡长；行政长官 (初中英语单词)
- instance [´instəns] n.例子，实例，例证 (初中英语单词)
- instrument [´instrumənt] n.仪器；手段；乐器 (初中英语单词)
- account [ə´kaunt] vi.说明 vt.认为 n.帐目 (初中英语单词)
- remarkable [ri´mɑ:kəbl] a.值得注意的；显著的 (初中英语单词)
- description [di´skripʃən] n.描写 (初中英语单词)
- virginia [və´dʒinjə] n.佛吉尼亚(州) (初中英语单词)
- maintain [mein´tein] vt.维持；保持；继续 (初中英语单词)
- existence [ig´zistəns] n.存在；生存；生活 (初中英语单词)
- anxious [´æŋkʃəs] a.担忧的；渴望的 (初中英语单词)
- charge [tʃɑ:dʒ] v.收费；冲锋 n.费用 (初中英语单词)
- considerable [kən´sidərəbəl] a.重要的；值得重视 (初中英语单词)
- effective [i´fektiv] a.有效的；有力的 (初中英语单词)
- inquiry [in´kwaiəri] n.询问；质询；调查 (初中英语单词)
- overcome [,əuvə´kʌm] vt.战胜，克服 (初中英语单词)
- equally [´i:kwəli] ad.相等地；平等地 (初中英语单词)
- complicated [´kɔmplikeitid] a.结构复杂的；难懂的 (初中英语单词)
- mischief [´mistʃif] n.伤害；故障；调皮 (初中英语单词)
- research [ri´sə:tʃ] n.&vi.调查；探究；研究 (初中英语单词)
- facility [fə´siliti] n.容易；熟练；灵巧 (初中英语单词)
- construction [kən´strʌkʃən] n.建设；修建；结构 (初中英语单词)
- arrangement [ə´reindʒmənt] n.整理；排列；筹备 (初中英语单词)
- properly [´prɔpəli] ad.适当地；严格地 (初中英语单词)
- driven [´driv(ə)n] drive 的过去分词 (初中英语单词)
- extent [ik´stent] n.长度；程度；范围 (初中英语单词)
- motion [´məuʃən] n.手势 vt.打手势 (高中英语单词)
- cavity [´kæviti] n.洞，窝；(人体)腔 (高中英语单词)
- representation [,reprizen´teiʃən] n.描写；表现(法) (高中英语单词)
- telescope [´teliskəup] n.望远镜 (高中英语单词)
- diameter [dai´æmitə] n.直径 (高中英语单词)
- astronomer [ə´strɔnəmə] n.天文学家 (高中英语单词)
- fertile [´fə:tail] a.肥沃的；有繁殖力的 (高中英语单词)
- regularly [´regjuləli] ad.有规律地；经常地 (高中英语单词)
- bearing [´beəriŋ] n.举止；忍耐；关系 (高中英语单词)
- subordinate [sə´bɔ:dinət] a.次的，附属的 n.部属 (英语四级单词)
- overwhelming [,əuvə´welmiŋ] a.压倒的；势不可挡的 (英语四级单词)
- magnitude [´mægnitju:d] n.宏大；重要性；大小 (英语四级单词)
- incapable [in´keipəbəl] a.无能力的；不能的 (英语四级单词)
- eclipse [i´klips] n.丧失 vt.食；蒙蔽 (英语四级单词)
- requisite [´rekwizit] a.需要的；必要的 n.必需品 (英语四级单词)
- treatise [´tri:tiz, -tis] n.(专题)论文 (英语四级单词)
- exceeding [ik´si:diŋ] a.超越的，非常的 (英语四级单词)
- aperture [´æpətjuə] n.孔；口径 (英语四级单词)
- supremacy [sju´preməsi] n.优越性；最高地位 (英语四级单词)
- miller [´milə] n.磨坊主；铣床(工) (英语四级单词)
- polish [´pəuliʃ] a.波兰(人)的 n.波兰语 (英语四级单词)
- lengthen [´leŋθən] v.(使)变长，延伸 (英语四级单词)
- shorten [´ʃɔ:tn] v.缩短，变短 (英语四级单词)
- mathematics [,mæθə´mætiks] n.数学 (英语四级单词)
- outcome [´autkʌm] n.结果；后果；成果 (英语四级单词)
- observatory [əb´zə:vətəri] n.天文台；气象台 (英语六级单词)
- photographic [,fəutə´grɑ:fik] a.摄影(术)的；逼真的 (英语六级单词)
- equatorial [,ekwə´tɔ:riəl] a.赤道的，近赤道的 (英语六级单词)
- dublin [´dʌblin] n.都柏林 (英语六级单词)
- satisfactorily [sætis´fæktərili] ad.令人满意地 (英语六级单词)
- uniformity [,ju:ni´fɔ:miti] n.同样；一致(性) (英语六级单词)
- mathematical [,mæθə´mætikəl] a.数学的；精确的 (英语六级单词)
- fitting [´fitiŋ] a.适当的 n.试衣 (英语六级单词)
- first-class [´fə:st-´klɑ:s] a.头等的 ad.乘头等车 (英语六级单词)
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