[20] Professor Challis, of the Cambridge Observatory, directing the Northumberland telescope of that institution to the place assigned by Mr. Adams’s calculations and its vicinity on the 4th and 12th of August 1846, saw the planet on both those days, and noted its place (among those of other stars) for re-observation. He, however, postponed the _comparison_ of the places observed, and not possessing Dr. Bremiker’s chart (which would at once have indicated the presence of an unmapped star), remained in ignorance of the planet’s existence as a visible object till the announcement of such by Dr. Galle. [21] For several interesting details of Comets, see “Destruction of the World by a Comet,” in _Popular Errors Explained and Illustrated_, new edit. pp. 165-168. [22] The letters of Sir Isaac Newton to Dr. Bentley, containing suggestions for the Boyle Lectures, possess a peculiar interest in the present day. “They show” (says Sir David Brewster) “that the _nebular hypothesis_, the dull and dangerous heresy of the age, is incompatible with the established laws of the material universe, and that an omnipotent arm was required to give the planets their positions and motions in space, and a presiding intelligence to assign to them the different functions they had to perform.”--_Life of Newton_, vol. ii. [23] The constitution of the nebulæ in the constellation of Orion has been resolved by this instrument; and by its aid the stars of which it is composed burst upon the sight of man for the first time. [24] Several specimens of Meteoric Iron are to be seen in the Mineralogical Collection in the British Museum. [25] _Life of Sir Isaac Newton_, vol. i. p. 62. [26] _Description of the Monster Telescope_, by Thomas Woods, M.D. 4th edit. 1851. [27] This instrument also discovered a multitude of new objects in the moon; as a mountainous tract near Ptolemy, every ridge of which is dotted with extremely minute craters, and two black parallel stripes in the bottom of Aristarchus. Dr. Robinson, in his address to the British Association in 1843, stated that in this telescope a building the size of the Court-house at Cork would be easily visible on the lunar surface. [28] Mr. Hopkins supports his Glacial Theory by regarding the _Waves of Translation_, investigated by Mr. Scott Russell, as furnishing a sufficient moving power for the transportation of large rounded boulders, and the formation of drifted gravel. When these waves of translation are produced by the sudden elevation of the surface of the sea, the whole mass of water from the surface to the bottom of the ocean moves onward, and becomes a mechanical agent of enormous power. Following up this view, Mr. Hopkins has shown that “elevations of continental masses of only 50 feet each, and from beneath an ocean having a depth of between 300 and 400 feet, would cause the most powerful divergent waves, which could transport large boulders to great distances.”