Popular Science Monthly/Volume 1/October 1872/The Transit of Venus
SOME of the world's greatest benefactors have worked with young minds, and one of the most remarkable discoveries of astronomical science was made by a company of English students in the best days of youth. We refer to the transit of Venus across the disk of the sun.
Our readers have doubtless noticed that Congress has already made provision for the scientific observation of the transit in 1874. The subject will soon engage the attention of astronomers, for the phenomenon furnishes us with the most important elements of astronomical knowledge. By the visible movement of the planet across the sun's centre, we are enabled to determine the sun's horizontal parallax, or the difference between the real and apparent position of the sun, and thereby to correctly calculate the distance of the earth and the planets from the sun, and the magnitude of the heavenly bodies. No person now living ever saw the transit, nor will any of the present inhabitants of the earth, who see the wonderful visions of 1874 and 1852, ever behold them again.
The transits of Venus occur alternately at intervals of eight, one hundred and five and a half, and one hundred and twenty-one and a half years. The last transit took place in 1769, before the American Republic had an existence, the next will occur in 1874, and the last that we shall ever see, in 1852. Nearly a century and a quarter will then pass away, to that strange-looking date 2004, ere the beautiful planet will impart her revelation to the astronomer on the sun's reflected image.
About the year 1635 there might have been found, in an obscure village near Liverpool, a young enthusiast of science, who, like Ferguson, turned away from the ordinary pastimes of youth to study the sublimities of the celestial scenery. He was beloved by all for his amiable disposition and his stainless life. Before he reached the age of eighteen he had mastered all the known problems of astronomical knowledge.
His name was Jeremiah Horrox. His father was a man of moderate means, but sympathized with his son's studious turn of mind, and, before the year 1633, placed him at Emanuel College, Cambridge.
The stormy times of the English Revolution were approaching. During the period in which the court and Parliament were occupied in the disputes that lost the first Charles his throne, four men (three of them were youths, and all of them intimately acquainted with each other) were employed in advancing the theory and practice of astronomy. They were, William Wilbon, William Gascoygne, James Crabtree, and Jeremiah Horrox, the subject of this sketch.
Possessing a sensitive, responsive nature, and always happier in loving companionship, the boy-astronomer Horrox made of James Crabtree, a youth in years but a sage in knowledge, a bosom-friend.
Horrox had but scarcely passed into his teens, before he became interested in the fact that the tables of Kepler indicated the near approach of the transit of Venus across the disk of the sun. It was a sight that no human eye had ever seen, and one which, if any human eye could see, would confirm all the deductions of the great German and Danish astronomers.
Often at night, as the boy Horrox stood before moonrise, gazing at the stars, and saw Venus—the Lucifer and Hesperus of the old classic poets—burning with a clear, steady flame, and casting a dim shadow over the vernal and midsummer fields, the thought would come to him that perhaps he, first among all the dwellers on the face of the earth, might see the planet, like a celestial messenger, darkening the solar centre.
The thought grew upon him, and haunted his waking dreams. In the hours that others spent in relaxation from toil, he studied and ciphered to see if the problems by which Kepler had fixed the date of the event had been accurately solved. The marvellous boy found an inaccuracy in the tables. Again and again he recast the figures of the great astronomer, with the same result. He calculated and recalculated the problems, until he himself wrought out a table by which it appeared that the next transit would take place on December 4, 1639.
We read of student-heroes, but what a proposition was this for a boy to demonstrate! Would the calculation indeed be verified by the event itself? Would the vision withheld from philosophers and sages, from the gray dawn of time, be first revealed to the eye of a boy—an humble boy?
Gassendi had noted the transit of Mercury a few years previously, the first that had ever been seen, and men of learning were discussing the discovery. Horrox aspired to follow up the triumph of Gassendi. He had proved the deductions of Kepler to be inaccurate, and he knew that he alone possessed the true knowledge of the phenomenon.
The imaginative years of youth flew by; his college-days passed, bringing him to the verge of manhood, and the looked-for time drew near.
Horrox met his young companions in science at times, and compared his astronomical observations with theirs, but to only one of them, his chosen friend Crabtree, did he confide the discovery that he had made of the near approach of the transit.
The memorable year arrived at length, and the memorable day came round. It was the Sabbath, a bright, shining day, clear and cool. In a room nearly dark sat the young astronomer, now twenty years of age. Engaged in devout thoughts, he awaited the fulfilment of his sublime dream. On a table before him lay a white sheet of paper on which to receive the sun's reflected image, over which the shadow of the planet would move like a dark spot, if indeed the boy's calculation were correct.
The sun mounted the deep-blue sky. The paper lay spotless before the expectant youth; no shadow broke the rim of its circle, and the hour for religious worship came.
The youth hears the call of the church-bells. Shall he heed it? Before he shall return from the house of God, a cloud may overcast the sky, and the celestial disclosure may be lost for a century!
He asks his conscience what he must do. The inward voice seems to tell him that the Creator himself is more worthy of worship than the phenomena he has instituted of admiration. He resolved, if need be, to lose the vision, and keep his eye single to the glory of God alone.
When he returned from the service, he went to the darkened room. The sun was still shining clearly. He approached the paper. It was there—the round shadow on the luminous image.
He sat down, overcome with the fulness of his emotions. The shadow crept slowly along the bright centre, like the finger of the Invisible. Then he knew that the great principles of astronomy were true, and he saw that a new revelation of scientific truth awaited mankind.
There are moments in human experience that repay the toils and struggles of a lifetime. Such were those of Galileo when he raised the newly-made telescope to the heavens; such were those of Rittenhouse, when, a century after the discovery of Horrox, he saw the shadow of Venus again crossing the disk of the sun; and such were those that the boy-astronomer himself felt as he watched the dark spot—the mighty shadow of a planet in the far abyss of space almost imperceptibly stealing across the circumference of the reflected circle on the paper. The sublimity of the youth's vision was as grand as the moral greatness of his soul.
His friend Crabtree, to whom he had communicated the secret, made the same discovery, by the same means, in a different place of observation.
The report of the discovery awakened a new interest in astronomical science throughout the world. Horrox was censured by men of culture for suspending his observations during the Sabbath service. He answered: "I observed the sun from sunrise to nine o'clock; again a little before ten, and lastly at noon, and from one to two o'clock—the rest of the day being devoted to higher duties!"
His work was ended. He fell a martyr to science, at the age of twenty-two. His companions in astronomical study also perished at an early age, two of them in the civil wars, and one of these at Marston Moor, fighting in defence of the crown.
The twilight of his young life was serene and cloudless. As his bodily strength decayed, he felt that his soul would soon rise in triumph over the glittering orbs on high, and join the pure in heart.
Nearly one hundred and thirty years passed before the transit of Venus was again visible. A transit had indeed occurred in 1761, but it did not fall within the observation of the astronomer.
The transit in 1709 was eagerly looked for because it was predicted. Expeditions were fitted out by the British, French, and Russian Governments, that it might be observed from widely-distant quarters of the globe. These went to Cape Wardhus, Kola, Cajaneburg, Otaheite, Fort Prince of Wales on the northwest of Hudson's Bay, St. Joseph and Santa Anna in California. The ingress of the planet was seen at almost all the observatories of Europe, the egress at Petersburg, Yakutsk, Uanilla, Batavia, Pekin, and Orenburg.
One of the principal observers, and perhaps the astronomer whose published observations were most highly valued, was David Rittenhouse. He, too, became an astronomer in boyhood, and used to calculate eclipses on the fences and on his plough-beam, when he stopped to rest in the field.
He, too, expectantly awaited the phenomenon, studying the theories and deductions that it involved by day and dreaming of them by night. He was assigned by the American Philosophical Society to Norriton, Pennsylvania, as his place of observation.
Rittenhouse possessed a highly-imaginative and sensitive nature; and when he saw, on the calm June day, the planet like a shadow, creeping, as it were, slowly along the edge of the solar disk, he became for some moments unconscious, overawed by the sublimity of the vision.
The transit of Venus, in 1874, occurs after an interval of one hundred and five and a half years.
|1639, December 4th (N.S.)||121½ years|
|1761, June 5th|
|1761, June 5th||8 years.|
|1769, June 3d|
|1769, June 3d||105½ years.|
|1874, December 8th|
Venus, being the second planet from the sun, and the larger of the two inferior planets having their orbits within that of the earth, appears to the earth the most luminous of all the planetary stars, her light at the period of her greatest splendor being so intense as to cast a shadow. She is seen in her full orbit beauty in regions under the equator at the period of her greatest elongation. Her telescopic appearance is interesting, lofty mountains breaking her luminous circle. During her transits her atmosphere is distinctly visible.
Extensive preparations are making, in England and on the Continent, for observing the transit in 1874 and 1882, which will afford the means of the most careful and accurate results.
- Congress has appropriated $150,000 to aid the observations, and has placed the United States Navy at the disposal of Messrs. Pierce, Henry, and Sands, to be employed for the purpose.
- The parallax of the sun, moon, or any planet, is the distance between its true and apparent place in the heavens, the true place of any celestial object being that in which it would appear if seen from the centre of the earth.
- The year 1769, the birth-year of Humboldt, Cuvier, and Napoleon, is marked in the calendar of science by unusual achievements in the infant branches of experimental investigation. Chemistry had emerged from the mystical stage of alchemy, and was planted upon its firm inductive basis. Bergmann had just made the first analysis ever made of mineral waters. Black, Cavendish, and Priestley, had commenced investigations into the nature of different kinds of air; and, in 1769, Scheele first discovered the existence of phosphate of lime in bones. The experiments of Bakewell in sheep-breeding, the first step in the art of improving stock, which has been carried to such perfection during the last hundred years, also date their success from 1739.—Ed.