In his own words, Sir John Herschel describes his aim in traveling to South Africa:
I resolved to attempt the completion ofa survey of the whole surface of the heavens, and for this purpose to transport into the other hemisphere the same instrument which had been employed in this, so as to give a unity to the results of both portions of the survey, and to render them comparable with each other ... Having disembarked the instruments [a reflecting telescope of18Y4 inches clear aperture and 20-feet focal length and a telescope of five inches aperture and seven feet focal length, used for the measurement ofdouble stars]... my next care was to look out for a comfortable residence in a locality suitable for their erection. This I was fortunate enough speedily to find at the mansion ofa Dutch proprietor, W.A. Schonnberg, Esq., bearing the name ofFeldhuysen, or Feldhausen, about six miles from Cape Town, in the direction ofWynberg, a spot charmingly situated on the last gentle slope at the base of Table Mountain...
Sir John Herschel writes of Feldhausen:
... well sheltered from dust, and, as far as possible from wind, by an exuberant growth ofoak and fir timber; far enough removed from the [Table] mountain to be, for the most part, out of reach of annoyance from the clouds which form so copiously over and around its summit, yet not so far as to lose the advantage of the reaction of its mural precipices against the south-east winds which prevail with great violence during the finer and clearer months, but which seldom blow home to the rock on this side .
Accompanying John Herschel and his family to the Cape, was his assistant John Stone.
In England, Sir John Herschel had engaged the services of an attendant for the purpose of working the sweeping, and other mechanical movements, of the Reflector during the observations, and Shrouds ofthe Night executing any necessary repairs. John Stone, the person so engaged, to the useful,
78 and, indeed, indispensable qualifications ofa ready mechanic, whether in wood or iron work, joined that ofexperience in this particular employment, having performed that office for me during a considerable portion of my review of the northern heavens, with undeviating steadiness and regularity, as he continued to do during the whole of that of the southern, without once absenting himself from his duty.
John Herschel would scan the skies, searching for new objects, by "sweeping" of the sky with his reflecting telescope. He would move the telescope (Figure 40) in zones of 3 degrees breadth (the equivalent of six full moons). These observations were executed "...in the absence of the moon, on all occasions when weather permitted, and the definition of the stars was such as to render it worth while to do so."
John Herschel had brought with him three metal mirrors for use in his reflector telescope:
... one made by my Father, and used by him in his 20-feet sweeps, and other observations; one made by myself, under his inspection and instructions; and one which I ground and figured subsequently, but which was cast at the same time, and from the same metal as that last mentioned. They are each I8Y4 inches ofclear diameter of polished surface, and all, so far as I am able to judge, equally reflective when freshly polished, and in every respect similar in their performance.
(In Herschel's day, the mirrors in reflecting telescopes were made of metal, usually speculum metal, an alloy of copper and tin. Small quantities of other metallic elements such as arsenic would make the metal whiter and more reflective. Modern telescope mirrors usually consist of glass, Pyrex, quartz or low expansion ceramics upon which coatings of silver or aluminum are deposited in vacuum conditions.)
Sir John Herschel describes the famous dark "Coalsack" in the southern sky, as follows:
. that singular vacuity on the south following side of the [southern] cross, called the "Coal-sack," a pear-shaped oval, whose greatest length is about 8 degrees,
and breadth 5 degrees, the longer axis being nearly parallel to the line joining a and P Crucis ... As this is always regarded by voyagers and travelers as one ofthe most conspicuous features ofthe southern sky, it may not be irrelevant to state a few particulars as to its telescopic constitution. It is by no means entirely devoid of stars ... Its striking blackness is, therefore, by no means owing to an absolute want of telescopic stars, but rather to its contrast with the very rich portion ofthe Milky Way adjacent...
Sir John Herschel's observations of the Magellanic Clouds opened to astronomers the detailed structure or morphology of these objects for the first time.
Of the Nubecula Major and the Nubecula Minor (the Large and Small Magellanic Clouds), Sir John Herschel comments:
The general appearance of these objects to the naked eye in a clear night and in the absence ofthe moon (whose light completely effaces the lesser and almost also the larger of them), is that of pretty conspicuous nebulous patches of about the same intensity with some ofthe brighter portions ofthe milky way.
When examined through powerful telescopes, the constitution ofthe Nubeculae, and especially ofthe Nubecula Major, is found to be of astonishing complexity.
Herschel compiled a preliminary catalogue of 1163 stars, nebulae and clusters of stars in the Magellanic Clouds.
He sketched the Magellanic Clouds with extraordinary perceptiveness, using a lamp-light and the naked eye.
I consider, therefore, that it will not be irrelevant to lay before the reader such representations as I have been able to make of them, entirely without telescopic aid, when seated at a table in the open air, in the absence of the moon, and with no more light than absolutely necessary for executing a From Seeds to Stars drawing at all. 81
Herschel identified spiral structure in the Large Magellanic Cloud as well as a central bar, which we shall further explore in Chapter 11. Sir John Herschel uses rich imagery ("an axis of light") to describe the bar which he visually discerned in that object.
We are most grateful to astronomer David Malin for drawing our attention to the following quote by Sir John Herschel:
To the naked eye ... the greater nubecula [the Large Magellanic Cloud] exhibits the appearance ofan axis of light (very ill-defined indeed, and by no means strongly distinguished from the general mass) which seems to open out at its extremities into somewhat oval sweeps ...
The monumental survey of the southern starry vaults by Sir John Herschel was published in 1847, in a volume entitled: "Results of Astronomical Observations made during the years 1834, 5, 6, 7, 8, at the Cape of Good Hope; being the completion of a telescopic survey of the whole surface of the visible heavens, commenced in 1825."
The survey lists 1708 nebulae and clusters and 1202 double stars. Herschel had swept the entire southern sky in only four years (1834-38). The sheer amount of work in the catalogues alone which are contained in the above volume, leaves the reader almost gasping for breath. Then, there were his outstanding astronomical drawings (Figures 41-43). Her-schel would prepare grids for his drawings, carefully positioning stars on these grids, before sketching the object itself - such as the Orion Nebula - on these "working skeletons." Herschel mentions using a lamp-light at the telescope to produce his masterful drawing of the Orion Nebula (Figure 42). Extraordinary patience, indeed: from January 1835 to December 1837 the grid for the drawing of the Orion Nebula was painstakingly laid out and carefully corrected.
In addition to the above, John Herschel used the method of "star gauging" to establish the distribution of stars in our Milky Way. "Star gauging" consists of counting the number of stars in selected circular fields of the telescope and then adding their sums to obtain an aver-Shrouds of the Night age (or mean) count. These gauges revealed striking differences in the density of stars in vari-
82 ous parts of the sky. Herschel gauged or counted 68 948 stars in 2299 different telescopic
fields and noted that his star counts increased toward the plane of our Galaxy. "Nothing can be more striking," Sir John wrote, "than the gradual, but rapid increase of density on either side of the Milky Way as we approach its course."
Below follows a few of his descriptions of the districts of the southern Milky Way:
Here the Milky Way is composed of separate, or slightly, or strongly, connected clouds of semi-nebulous light; and, as the telescope moves, the appearance is that of clouds passing in a scud as the sailors call it ... The Milky Way is like sand, not strewed evenly as with a sieve, but as if flung down by handfuls (and both hands at once), leaving dark intervals, and all consisting of stars ... down to nebulosity, in a most astonishing manner.
After an interval of comparative poverty, the same phenomenon, and even more remarkable. I cannot say it is nebulous. It is all resolved, but the stars are inconceivably numerous and minute. There must be millions on millions, and all most unequally together...
...we see, foreshortened, a vast and illimitable area scattered over with discontinuous masses and aggregates of stars in the manner of the cumuli of a mackerel sky, rather than of a stratum of regular thickness .
In his 1847 volume, John Herschel pays much attention to the classification of the nebulae.
Eneas Sweetland Dallas (1828-1879) is believed to be the author of a book entitled Three Essays, a copy of which was owned by Sir John Herschel. In the Three Essays, published in 1863, we read these words:
Every principle ofclassification is a conception to be applied to the plan of nature for verification. The mode in which a classification is verified, or found truly to Shrouds ofthe Night represent the plan of nature, is in finding the characteristics chosen as distinctive
86 ofthe classes, orders, and genera, predominant in the same degree in nature as in the classification - so predominant that when we speak ofthe qualities which distinguish the classes we find we speak of truths of wider generality than when we speak ofthe qualities which distinguish the orders, and so forth ... a true system of classification, such as shall be verified in nature, reduces the mass of facts from a confusion which none can follow to an order which none can mistake.
In the same chapter, the author of Three Essays quotes Sir John Herschel as follows:
"Classification in such a case," says Sir J. Herschel, "is only another word for the announcement of general laws, the result of inductive observation - results, that is to say, of a more elevated order than those which depend on a mere remarking of general resemblance, or even on the specifications of particular arbitrary selected points on which logicalproofof such resemblance can be rested."
Before we can enter into any thing which deserves to be called a general and systematic view of nature, it is necessary that we should possess an enumeration, ifnot complete, at least ofconsiderable extent, of her materials and combinations; and that those which appear in any degree important should be distinguished by names which may not only tend to fix them in our recollection, but may constitute, as it were, nuclei or centers, about which information may collect into masses. The imposition ofa name on any subject ofcontemplation, be it a material object, a phenomenon of nature, or a group offacts and relations, looked upon in a peculiar point of view, is an epoch in its history of great importance.
wrote John Herschel in his book A Preliminary Discourse on the Study of
Natural Philosophy first published in 1830.
Embarking upon unexplored scientific territories, Sir John Herschel expresses his thoughts thus:
The character ofthe true philosopher is to hope all things not impossible, and to believe all things not unreasonable. When once embarked on any physical research, it is impossible for anyone to predict where it will ultimately lead him.
The true answer of science is that which again is at once the parallel and the illustration of the language of the apostle, "The mysteries of knowledge, which in other ages were not made known unto the sons of men, are now revealed, and will be still more revealed to those whom God has chosen." Or still again, "The students of science are as messengers from Heaven to earth to make such stupendous announcements, that they may claim to be listened to when they repeat in every variety of urgent instance, that these are not the last announcements they have to communicate; that there are yet behind, to search out and to declare, not only secrets of nature which shall increase the wealth and power of men, but truths which shall ennoble the age and country in which they are divulged and, by dilating the intellect, react upon the moral character of man-kind."
While at the Cape, Sir John Herschel produced a most impressive set of drawings using a camera lucida:
The camera lucida superimposes by means of a prism a virtual image of any view on the plane of a drawing board so that it can be traced by an artist. There is no projected image, but only a virtual one. In other words, by looking into the prism of the camera lucida at just the correct angle, two images enter the eye; one, of the landscape or object to be sketched, the other of the pencil and paper with which the artist intends to draw with. The resulting effect is that, with the camera lucida, the eye perceives the scene to actually lie superimposed on the drawing paper - while in reality it does not. The superposition of scene and drawing paper affords the artist the opportunity to trace nature in perspective, using a pencil. Only the artist sees the superposition of both scene and paper; an on-looker would not see any virtual image on the drawing paper at all. What added to its great use by artists was that the camera lucida was a highly portable device.
Writes N.S. Dodge: "Like a child, he went to Nature's school to learn what she had to teach."
Sir John Herschel was a most extraordinary observer. His interests spanned cosmic horizons in the broadest of senses, making contributions to ornithology, geology, botany, mathemat-Shrouds of the Night ics and chemistry - apart from his chief passion, astronomy. His camera lucida sketches
88 (some of which are reproduced in Figures 44-46) show a meticulous attention to detail.
fir" tar-'. a inm i * '\mW Wn fir" tar-'. a
,■--«»Ssa ■■ Z y? Wtat y.A, ' •. - i ■ ■ »kV i I ' ,"i,■ 3
,■--«»Ssa ■■ Z y? Wtat y.A, ' •. - i ■ ■ »kV i I ' ,"i,■ 3
WRwwPi'i1! Jjii pi^igfc
■ '■■ • A- ■.•XVv¿»-.v •».• i-r'H
WRwwPi'i1! Jjii pi^igfc
■ '■■ • A- ■.•XVv¿»-.v •».• i-r'H
P^SIlPli msfejjfc;:, vm^Mi iU
He was keenly aware of the interface between observation and theory:
"First let, me mention," Sir John Herschel writes "that if we should hope to make any progress in investigations of a delicate nature, we ought to avoid two opposite extremes, of which I can hardly say which is the most dangerous. If we indulge a fanciful imagination and build worlds of our own, we must not wonder at our going wide from the path of truth and nature; but these will vanish like the Cartesian vortices that soon gave way when better theories were offered. On the other hand, if we add observation to observation, without attempting to draw, not only certain conclusions, but also conjectural views from them, we offend against the very end for which only observations ought to be made."
In the 1847 volume, Herschel concludes:
The record of its site [where the Reflector stood] is preserved on the spot by a granite column erected after our departure by the kindness of friends, to whom, as to the locality itselfand to the colony, every member of my family had become, and will remain, attached by a thousand pleasing and grateful recollections of years spent in an agreeable society, cheerful occupation, and unalloyed happiness.
In the space of only four years at the Cape, John Herschel had accomplished more than some may hope to achieve in a lifetime. The Herschels began their sea voyage back to England on 11th March 1838.
In her book entitled The Herschels and Modern Astronomy, Agnes M. Clerke sums up John Herschel's "southern sojourn" thus:
... enchanting scenery, translucent skies, blossoming glens and hillsides worthy of Maeldune's Isle of Flowers, contributed to render his southern sojourn a radiant episode. He wrote of it... as "the sunny spot in my whole life, where my memory will always love to bask."But "the dream," he added, "was too sweet not to be Shrouds ofthe Night dashed by the dread ofawakening." That spell was broken when in the middle of
92 March, 1838, he sailed in the Windsor Castle for England.
Star clusters, galactic nebulae and galaxies were catalogued by the Herschels, and descriptions were provided. Nebulae were classified according to "magnitude" (great, large, middle, small, minute), "resolvability" (discrete, resolvable, granulated, mottled and milky) as well as "brightness," "roundness" and "condensation" (see Figure 47). One nebula might be "middle-sized, bright, round, stellate, resolvable" while another might be "small-sized, dim, elongated, discoid, milky." Sir John Herschel also applied the term "falcated" to certain nebulae in the form of a sickle (falcated is derived from the Latin falcatus, sickle).
What a tremendous source of joy it is to personally hold and to examine many of the Herschel drawings of the nebulae in one's hand, at the library of the Royal Astronomical Society of London. An astonishing 4630 objects were actually discovered by William and John Herschel.
The morphologist needs to see, to examine, important structural features of galaxies (such as resolving stars in the spiral arms of myriads of "nebulae") - this awaited the dawn of the photographic era. The classification of galaxies - grouping them into different families of form or morphology - is both a science and an art. We can say that it is a science, because the appearance or form of galaxies is determined by the scientific processes that took place as each galaxy formed and developed with time. Although classification surely has a scientific
Was this article helpful?