Caroline

A greater ray of hope than William's invitation Caroline could not have dreamed of. Since her father's death, she had fallen, as she put it in her memoir, in ''a kind of stupefaction.'' Her father had supported her attendance at the garrison school—despite the fact that women of her station and era did not commonly learn to read and write—and had taught her to play the violin. After his death, although she longed for a job as a governess, her activities were constrained to sewing and knitting, and helping her mother keep house. Her mother curtailed her efforts at self-improvement. As Caroline saw it, ''she had cause for wishing me not to know more than was necessary for being useful in the family; for it was her certain belief that my brother William would have returned to his country, and my eldest brother not have looked so high, if they had had a little less learning.''10

At the age of 22, the unusually short-statured but vigorous and capable youngest daughter of the family felt utterly hopeless and frustrated at her prospects. William's extraordinary suggestion roused her to begin practising for a musical career—but in secret, for the prickly Jacob, her older brother, ''began to turn the whole scheme into ridicule.'' When family members were away from home, she stuffed a gag between her teeth, and imitated ''the solo parts of concertos, shake and all,'' as she had heard them played on the violin. ''[I]n consequence I had gained a tolerable execution before I knew how to sing,'' she explained later.11

Caroline's mother acquiesced to the plan with difficulty, but Herschel made it more palatable when he arrived in Hanover to pick up his sister. ''My mother had consented to my going with him, and the anguish at my leaving her was somewhat alleviated by my brother settling a small annuity on her, by which she would be enabled to keep an attendant to supply my place,'' Caroline wrote later. Herschel would support members of his family in a similar way throughout his life.12

Brother and sister arrived at Herschel's house in Bath in late August 1772. Bath's high season, which ran from fall to Easter, was just beginning. William and Alexander, who lodged with William, were busy with rehearsals, and William also with his many private students, young ladies and men. Caroline, who did not yet speak English, found she must manage without much help. At the breakfast table, William explained bookkeeping and other aspects of managing the household. Caroline was sent out alone to do the grocery shopping—although she discovered later that Alexander trailed behind her to make sure she returned home safely.

All through the winter Caroline looked forward to the end of the busy season, when William would have more time for her own daily music lessons. She struggled with homesickness and loneliness, and complained in her memoir about her brother's ''hot-headed'' servant, who made her life difficult.13 But as spring approached, she observed that her brother's attention was tugging him in another direction. Her memoir records the dawning of a new passion for astronomy in William:

''The time when I could hope to receive a little more of my brother's instruction and attention was now drawing near,'' she wrote. ''But I was greatly disappointed; for, in consequence of the harassing and fatiguing life he had led during the winter months, he used to retire to bed with a bason of milk or glass of water, and Smith's 'Harmonics and Optics,' Ferguson's 'Astronomy,' &c, and so went to sleep buried under his favorite authors; and his first thoughts on rising were how to obtain instruments for viewing those objects himself of which he had been reading.''14

Herschel himself explained that his bed-time reading had led him from the study of music theory to astronomy. He wrote, ''The theory of Music being connected with mathematics had induced me very early to read in Germany all what had been wrote upon the subject of Harmony; & when, not long after my arrival in England the valuable Book of Dr. Smith's Harmonics came int[o] my hands I perceived my ignorance & had recourse to other authors for information by which means I was drawn on from one branch of the Mathematics to another. [...] Among other mathematical Subjects optics and Astronomy came in turn & when I read of the many charming discoveries that had been made by means of the telescope I was so delighted with the subject that I wished to see the heavens & Planets with my own eyes thro' one of those instruments.''15

Herschel's first telescopes were crude spyglasses that he and Caroline assembled in 1773 with lenses that he was able to order from manufacturers. Caroline, who had no inkling yet that her own lifework lay in astronomy rather than music, later wrote of her exasperation with the changing demands made of her: ''I was much hindered in my musical practice by my help being continually wanted in the execution of the various contrivances, and I had to amuse myself with making the tube of pasteboard for the glasses [glass lenses] which were to arrive from London, for at that time no optician had settled at Bath.''16

Herschel's preoccupation with seeing the stars and planets for himself dovetailed with the talent he and his brother Alexander obviously both had for mechanical invention, and led to his experimentation with new forms of telescopes. At first he worked with lens-based or "refracting" telescopes. He soon became dissatisfied with the lenses, however. As white light passes through a lens and is brought to a focus, the different colors composing the light disperse at different angles, so that a colored "halo" surrounds the image. In the late eighteenth century, lensmakers had not yet discovered a way to reduce this unwanted effect, called chromatic aberration.

"Reflecting" telescopes, based on mirrors or on a combination of mirror and lens, were known to give a less distorted view. In the fall of 1773 Herschel rented a reflecting telescope of a type known as a Gregorian, partly so he could use it and partly so he could take it apart and study its construction. In the Gregorian design, already about a hundred years old, a curved mirror at the rear of the telescope tube collects the light from the star or planet and reflects it back up the barrel of the instrument. This is the primary mirror, so called because it is the first to intercept the light from the sky. A smaller, curved secondary mirror is suspended in the barrel in front of the primary, blocking a small (and negligible) part of the incoming light. This secondary redirects the light from the primary back down the telescope and through a small hole in the primary, to a lens-based eyepiece at the back of the telescope. The user puts his eye to the back end of this telescope, as he or she would with a spyglass. (See figure 4.4 for an illustration of various telescope types mentioned in this chapter, including the Gregorian.)

Herschel liked the rented Gregorian telescope and wanted one of his own made — even bigger in diameter than the one he had rented, if possible. He understood that the true power of a telescope is determined by its aperture, the area of the primary mirror or lens collecting light from a distant object. A telescope with an opening of 4 inches diameter, for example, collects four

Figure 4.4 Types of telescope. In the Gregorian type of reflecting telescope, shown at left, light from the primary mirror is reflected to a curved secondary mirror, and from there to the eyepiece at the bottom of the telescope structure. The secondary mirror blocks a small part of the incoming light, but does not distort the image formed by the telescope (because the blocked light does not represent a specific geometric area of the source of light, but comes from the entire source). In the Newtonian design, shown in the middle panel, a flat secondary mirror directs the light to an eyepiece on the side of the telescope; aside from the difficulty of creating a perfectly flat secondary mirror, the design is similar to the Gregorian. In the Herschelian design, shown at right, the observer is rather awkwardly situated at the front end of the telescope. The advantage of the Herschelian design is that the light is only reflected once; upon reflection from a secondary mirror, some light inevitably would be lost. (Credit: Layne Lundstrom.)

Gregorian Newtonian Herschclian

Figure 4.4 Types of telescope. In the Gregorian type of reflecting telescope, shown at left, light from the primary mirror is reflected to a curved secondary mirror, and from there to the eyepiece at the bottom of the telescope structure. The secondary mirror blocks a small part of the incoming light, but does not distort the image formed by the telescope (because the blocked light does not represent a specific geometric area of the source of light, but comes from the entire source). In the Newtonian design, shown in the middle panel, a flat secondary mirror directs the light to an eyepiece on the side of the telescope; aside from the difficulty of creating a perfectly flat secondary mirror, the design is similar to the Gregorian. In the Herschelian design, shown at right, the observer is rather awkwardly situated at the front end of the telescope. The advantage of the Herschelian design is that the light is only reflected once; upon reflection from a secondary mirror, some light inevitably would be lost. (Credit: Layne Lundstrom.)

times as much light as one with an opening 2 inches in diameter, because its geometric area is four times greater. The bigger the primary, Herschel knew, the fainter the objects one could see with the telescope.

Herschel also knew that the magnifying power—which many people mistakenly assume is the measure of the quality of a telescope—is an indication only of the apparent size of the image formed. The magnification of the image depends on the eyepiece used, and telescopes usually come with a variety of interchangeable eyepieces to provide a range of magnifying power. (A higher power eyepiece will not improve a fuzzy image — it just creates a bigger fuzzy image. But a larger diameter telescope, even with a low-power eyepiece, improves the detail and crispness of the image.)

The price a local merchant quoted to make a larger aperture reflecting telescope seemed ''extravagant'' to Herschel, but he soon thought of a way around the problem. ''I formed the resolution to make myself one,'' he wrote, ''as, not aware of the difficulty, it appeared to me from some former mechanical attempts that with the assistance of Dr. Smith's optics I should be able, in time, to accomplish such a work.'' Herschel indeed underestimated the difficulties of obtaining high-quality mirrors and mounting them in good alignment, but he did not underestimate his own skill or perseverance. In a period of a few years in the late 1770s, he made more than 200 primary or objective mirrors before declaring himself satisfied with the results.17

Whether or not Herschel already dreamed of making his own discoveries, he knew at least from the history of astronomy in Dr. Smith's Compleat System of Opticks that improvements in telescopes often led to new insights, even in the study of familiar solar system objects such as Saturn. In the early 1600s, shortly after the first telescopes were developed, Galileo had noticed mysterious ''ears'' on either side of Saturn, which he thought might be stationary moons of that planet. In 1659, the Dutch astronomer and mathematician Christiaan Huygens, with an improved telescope, clarified that the ''ears'' were rings; then in the 1670s, Cassini, with his improved optics, found the gap in Saturn's rings and discovered new moons circling the planet, too. It was worth building better telescopes even to look at known objects.

Throughout the winter of 1773 and into the spring and summer of 1774, when he was not occupied with concerts and rehearsals, Herschel devoted every spare moment to making his own telescopes. Alex, when he was home, assisted him; Caroline refers to his particular talents at least twice in her memoir. She wrote, for example, that ''he took much pleasure to execute some turning or clockmaker's work for his brother.''18

To her dismay, Caroline found her housekeeping duties must evolve to accommodate the fact that virtually every room in the house was transformed into a workshop. Alex worked a lathe in one of the bedrooms, making eyepiece lenses. In the basement, William toiled over mirrors — ''speculum'' mirrors made of alloys of tin, copper, antimony, and silver. A local manufacturer cast the mirror blanks for him, but William ground them into precisely curved shapes before polishing them to a high gloss with silk soaked in a tar-like concoction. ''Every leisure moment was eagerly snatched at for resuming some work which was in progress, without taking time for changing dress, and many a lace ruffle was torn or bespattered by molten pitch,'' Caroline complained. At mealtimes William was absent-minded, ''contriving'' or sketching new apparatus. If he had many hours of manual polishing to do, Caroline skipped her own music practice and read to him from Don Quixote, Arabian Nights, or some novel.19

Herschel's reward for this unceasing effort and experimentation took the form of a Newtonian design telescope (see figure 4.4). The Newtonian design differs from the Gregorian in requiring only one curved or figured mirror instead of two: a flat secondary mirror near the middle or top of the telescope tube shunts the light from the primary mirror to an eyepiece at the side of the telescope. The aperture diameter of his first satisfactory telescope was about 4 % inches, which today would be typical of an amateur's first telescope.

On 1 March 1774, he inaugurated his first review of the heavens through this telescope, turning it first to the beautiful Orion nebula (see chapter 2, figure 2.7). His view of Saturn and its ring like ''two slender arms'' encircling the planet, he wrote in his memoir, gave him ''infinite satisfaction.''20 The seriousness of his purpose is evident from the fact that he no longer used his diary to record his observations, but began a separate astronomical journal.

Herschel found it increasingly difficult to keep his mind on his private music tutoring, concerts, and accompaniments. He wrote of this period in his memoir, ''Nothing seemed now wanting to compleat my felicity than sufficient time to enjoy my telescopes to which I was so much attached that I used frequently to run from the Harpsichord at the Theatre to look at the stars during the time of an act & return to the next Music.''21

As he sprinted to his telescope during borrowed intervals of time, Herschel's imagination was likely to dwell on the mountainous landscapes of the moon or the mottled, reddish surface of Mars. In the early years of his forays into astronomy, Herschel made mostly solar, lunar, and planetary observations, following the lead of his favorite textbook authors. He initiated a long-term series of observations of the planet Venus aimed at determining its diameter, its period of rotation, the nature of its surface, and whether or not the planet has an atmosphere. Bright white spots on Mars, that planet's icy polar caps, aroused his curiosity in 1777; repeated observations allowed him to observe their seasonal changes in size. Saturn, which he called ''one of the most engaging objects that astronomy offers to our view,'' he returned to again and again.22 Initially Herschel, like his contemporaries in astronomy, viewed solar system objects as the natural concern of the astronomer; he paid little attention to the more distant stars unless they called attention to themselves by varying in brightness or by moving with respect to the fixed pattern of stars. (Recall that Halley had found some examples of stars with ''proper motion,'' and that Wright had incorporated this finding in his models of the stellar system.) Later, Herschel himself was to open up the realm of the stars to exploration.

Herschel's self-education in astronomy and telescope construction is all the more remarkable considering that during the late 1770s his musical career was still gaining momentum. In 1776, he took on the responsibilities of Director of the Public Concerts at Bath. Meanwhile, Caroline's duties at home became more complex as William and Alexander turned their rented house into a telescope factory. In fact, her domestic burden increased in the late 1770s when her younger brother Dietrich, a high-spirited but irresponsible young man, came to live with his siblings following an abortive attempt to sail for a life of adventure in India. She was not a little relieved when he returned to Hanover in 1779. But musical demands on Caroline's time did not slacken. She became an accomplished singer and even received an invitation to perform at a festival in the city of Birmingham — although she declined it because she had decided not to sing in public unless her brother conducted.

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