A. ROSS, 



OPTICIAN, 



2, FEATHEESTONE BUILDINGS, HOLBOKN, 



Begs to call the attention of Observers with the Microscope to his 

 improved Instruments, a Catalogue of which may be had upon ap- 

 plication. 



Among the various advancements A. R. has effected is the extreme 

 enlargement of the aperture of the Microscope Object Glass, which is 

 its real effective improvement ; also an Achromatic Condenser of Light for 

 the Microscope, on a new combination of principles, for the illumination 

 of transparent objects, adapted for use, with the several Object Glasses 

 from I an inch to y'^ of an inch focal length inclusive. 



The object of this arrangement is to develop the defining powers of 

 Object Glasses, and, by a peculiar adjustment, to adapt the illumination 

 to the nature of the object and to the mode of mounting, whether dry or 

 in fluid, or in Canada balsam, so as to admit a greater quantity of light 

 with less glare, and, in consequence, to give a more distinct image with less 

 fatigue to the eye. The Microscope Stand, or mechanical part, has also 

 been arranged to ensure freedom from tremor and afford facility in use. 



A. R. also begs to announce, that from a laborious practical investi- 

 gation of the construction and manufacture of the Achromatic Astro- 

 nomical Telescope, he has arranged a new process for their production 

 which ensures the perfection of that important instrument ; also, that in 

 Terrestrial and Naval Telescopes, the contact surfaces of the Object 

 Glasses are united by a permanently transparent cement, which obviates 

 the loss of light by reflections, and prevents that decomposition of the 

 glass which generally occurs in Marine Telescopes. 



Since the invention of those prospectively useful arts, the Calotype and 

 the Daguerreotype, A. R. has investigated the forms of lenses necessary 

 to giye just representations of objects, and has succeeded in giving great 

 intensity to the image with fine and correct definition, both at the centre 

 and margin of the picture; also the visual and chemically acting foci are 

 made to coincide. 



A. R.'s Binocular Reading Glass prevents the fatiguing muscular exer- 

 tion of the eyes attendant on the use of Spectacles of the ordinary con- 

 struction, and preserves the eyes in repose during protracted application. 



ASTRONOMICAL AND SURVEYING INSTRUMENTS. 



BAROMETERS, HYGROMETERS, THERMOMETERS, &c., &c. 



CORNELIUS POULTON, 

 preparer of ©ftims for tije jaicrosrope, 



SOUTHERN HILL, READING, 

 BERKS. 



