Transit of Venus Observed in Yard of State House June 3, 1769

The year 1769 was memorable in the annals of astronomy, owing to the transit of Venus over the sun’s disc, which occurred June 3. Astronomers throughout the entire world were anxious to make an observation of this celestial phenomenon, which would not occur again until 1874.

The great interest centered in this observation arose from the fact that by means of it the distance between the heavenly bodies could be more accurately calculated. It was the belief that the transits of Venus afforded the best method of measuring the distance of the sun from the earth.

385This was a period of intense interest, and many expeditions were fitted out to observe the transit at different places in both the northern and southern hemispheres.

Mason and Dixon, the English astronomers, who gained undying fame as the surveyors of the boundary line between Pennsylvania and Maryland, started on a ship of war for their station on the southern hemisphere, but they were attacked by a French frigate and were compelled to return to port after a severe battle. Other expeditions became celebrated through the adventures to which they gave rise.

The transit of 1769 was visible in the Atlantic States and observations upon it were made under the auspices of the American Philosophical Society at Philadelphia. The most celebrated of all these observers was David Rittenhouse.

Benjamin Franklin had organized the society and in 1769 became the society’s first president. He was annually elected to that position for twenty-two years, being succeeded in 1791 by another Pennsylvanian, David Rittenhouse.

In 1768 the American Philosophical Society petitioned the Assembly of Pennsylvania for assistance to observe the transit of Venus, and the proposition was treated with liberality.

One hundred pounds was granted to enable the society to procure a reflecting telescope of two and a half or three feet focus and a micrometer of Dolland’s make, which had to be procured from England. They were purchased there by Dr. Franklin.

The society erected a wooden building as an observatory in the State House yard. This was of circular shape, and about twenty feet high, twelve to fifteen feet square and placed about sixty feet south of the State House.

On the morning of June 3 the sky was cloudless. The transit was observed from this building in the State House yard by Dr. John Ewing, Joseph Shippen, Dr. Hugh Williamson, Thomas Prior, Charles Thomson and James Pearson.

While they were thus engaged, David Rittenhouse, Dr. William Smith, John Sellers and John Lukens noticed the phenomena at Norriton, the home of the celebrated astronomer. Owen Biddle made an observation at Henlopen lighthouse.

Rittenhouse was already a member of the American Philosophical Society and made his observations for that society. He used a telescope and other instruments made by his own hands.

When he observed the contact, and the planet had fairly entered the sun’s disk, his emotions so overpowered him that he sank fainting to the ground, unable to bear the intense feelings of delight which attended the consummation of the long hoped for event. Rising from his exhaustion, he proceeded to measure the distance between the centers of the two bodies at stated intervals during the transit.

386The observations of Rittenhouse were received with interest by scientific men everywhere. Subsequently they were found to be nearly accurate and his computations placed him among the greatest of astronomers. The royal astronomer of England bore testimony to their value and another high authority said:

“The first approximately accurate results in the measurements of the spheres were given to the world, not by schooled and salaried astronomers who watched from the magnificent royal observatories of Europe, but by unpaid amateurs and devotees to science in the youthful province of Pennsylvania.”

On November 9 of the same year David Rittenhouse made an observation of the transit of Mercury, which was the fourth ever witnessed. About this time he also determined the difference of the meridians of Norriton and Philadelphia.

David Rittenhouse was without doubt the first inventor of a practical planetarium, erroneously called the “orrery,” an instrument so constructed as to exhibit the movements of the planets around the sun. In theory the idea was not new. Such an instrument had been made for the Earl of Orrery in 1715, but this was a mere toy and gave the movements of only two heavenly bodies.

Rittenhouse determined that he would make an elaborate instrument, based on scientific principles and on the astronomical calculations which he had prepared. After three years of labor, in 1779, the “Rittenhouse orrery” was completed.

This orrery was purchased by Princeton University for £300. The trustees of the College of Philadelphia were offended, but Rittenhouse immediately set to work and constructed a duplicate, which was purchased for the college by the proceeds of a series of lectures on astronomy by Dr. William Smith, provost of the college.

The second orrery was much larger than the original, but was constructed on the same model. This was sold for £400.

David Rittenhouse was elected one of the secretaries of the American Philosophical Society in 1771. He delivered a most elaborate address before the society February 23, 1775, entitled “An Oration on Astronomy.” This address was inscribed and dedicated to the delegates assembled in the Continental Congress. In 1790 he became one of its vice presidents.

On the death of Dr. Franklin he succeeded to the office of president, January, 1791, which office he held until his death, when he was succeeded by Thomas Jefferson.

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