To an object, then, of such vast importance to science, were proportioned the expectations of our Observers. But they could not fail to experience, at the same time, in common with their astronomical brethren in other parts of the world, a large portion of anxious apprehensions, lest a cloudy day—nay, even a solitary passing cloud,—should baffle entirely their exalted hopes, and destroy all the fruits of their arduous labours! Yet such an occurrence, as one or the other of these events, was evidently within the calculations of a probable incident. Mr. Rittenhouse participated largely in these blended hopes and fears. He had, for some time before, been laboriously employed in making the requisite preparatory observations and calculations: and, as Norriton was now rendered eminently conspicuous, by being fixed on as a principal site for observing the very interesting phænomenon so near at hand, he had been assiduously engaged, at the same time, in preparing and furnishing an Observatory at that place, suitable for the occasion. This he began to erect early in November, 1768,—“agreeably,” to use his own words, “to the resolutions of the American Philosophical Society;” but, through various disappointments from workmen and weather, he was not enabled to complete it till the middle of April, 1769.[111] ----- Footnote 111: It was not until the year 1786, that Mr. Rittenhouse built the house at the north-west corner of Arch and (Delaware) Seventh streets, in Philadelphia, where he resided during the remainder of his life: but probably it was some few years earlier that he erected his Observatory, a small but pretty convenient octagonal building, of brick, in the garden adjacent to his dwelling-house. Its situation was not an ineligible one, when the building was first put up: but its commodiousness and utility were probably much diminished, by the erection, not long afterwards, of some large houses near it; and it is presumable, that its usefulness in any degree, for the purposes of an Observatory, could have continued but a little while beyond the duration of its late proprietor’s life, by reason of the rapid increase of the number of lofty houses in the vicinity. Indeed it lately became extremely probable, on considering the great enlargement of Philadelphia within the last twenty-five years, that the future augmentation of the population and extension of improvements in this beautiful and hitherto flourishing city, would, in a very few years, render the late Observatory of Mr. Rittenhouse wholly useless for astronomical purposes; and, in the event of the surrounding ground and adjacent buildings being alienated from his family, improper for any other.