That reflecting telescopes of the descriptions now stated are original in their construction, appears from the uniform language of optical writers, some of whom have pronounced such attempts to be altogether impracticable. Sir David Brewster, one of the latest and most respectable writers on this subject, in the ‘Edinburgh Encyclopedia’ art _optics_, and in the last edition of his _appendix_ to ‘Ferguson’s Lectures,’ has the following remarks:--‘If we could dispense with the use of the small specula in telescopes of moderate length, by inclining the great speculum, and using an oblique, and consequently a _distorted_ reflection, as proposed first by La Maire, we should consider the Newtonian telescope as perfect; and on a large scale, or when the instrument exceeds 20 feet, it has undoubtedly this character, as nothing can be more simple than to magnify, by a single eye-glass, the image formed by a single speculum. As the _front view is quite impracticable_, and indeed _has never been attempted_ in instruments of a small size, it becomes of great practicable consequence to remove as much as possible, the evils which arise from the use of a small speculum,’ &c. The instruments now described have effectuated, in some degree, the desirable object alluded to by this distinguished philosopher, and the mode of construction is neither that of Sir W. Herschel’s front view, nor does it coincide with that proposed by La Maire, which appears to have been a mere hint that was never realized in the construction of reflecting telescopes of a small size. The simplicity of the construction of these instruments, and the excellence of their performance, have been much admired by several scientific gentlemen and others to whom they have been exhibited. Prior to the description of them in the Edin. Philos. Journal, they were exhibited in the Calton Hill Observatory, Edinburgh, in the presence of Professor Wallace, and another gentleman, who compared their performance with that of an excellent Gregorian. As this instrument is distinguished from every other telescope, in being used without a tube, it has been denominated ‘_The aerial reflector_.’ SECT. 4.--EARL OF ROSSE’S REFLECTING TELESCOPES.