Mr. A. Claudet on soma Stereoscopic Phenomena, 397 



Part 4. Sea-level Meteorological Journal. 

 Part 5. Reductions of above. 



Part 6. Plans, Sections, and Astronomical illustrations. 

 Parts 7, 8, 9. Condensed statement of results and conclusions in 

 Astronomy, Physics, Meteorology, Geology, Botany, and Navigation. 

 Part 10. Photographs illustrating the botany and geology of three 

 different levels in the Island. 



The original instructions of Prof. Piazzi Smyth had been purely 

 astronomical, and were to ascertain how much telescopic vision could 

 be improved by eliminating the lower third of the atmosphere. In 

 furtherance of this view, he erected the Sheepshanks equatorial of 

 the Edinburgh Observatory on Mount Guajara in Teneriffe at a 

 height of 8903 i^^t, and "found the space-penetrating power ex- 

 tended from mag. 10 to mag. 14, and so great an improvement in 

 definition, that a magnifying power of 240 could be used with more 

 satisfaction on the mountain, than one of 60 in Edinburgh. After 

 a month's experience of this station, he ascended to a higher one — 

 the Alta Vista — at a height of 10,702 feet on the eastern slope of 

 the Peak, and there erected the large equatorial of Cooke, lent for 

 the occasion by Mr. Pattinson of Newcastle. The definition was here 

 admirable, and the telescope equal, if not superior, to all the test 

 objects it was turned upon. A comparative hypsometric estimate 

 was not pQssible ; for although the observer had spent an equal 

 number of days to what he employed on the Peak, in trying to as- 

 certain the capabilities of the instrument at the house of its hospi- 

 table owner, on several visits, the cloudy atmosphere of Newcastle 

 had always prevented any good observations being made. 



An argument in favour, however, of the increase of height was 

 ascertained through means of radiation instruments, which indicated 

 almost as much improvement between 10,700 and 8900 feet, as be- 

 tween the latter height and the sea-level. This unexpected degree 

 is attributed by the author to the circumstance of the highest station 

 being almost clear of certain dry, hazy, or dusty strata of atmo- 

 sphere, which include and overtop the intermediate station, and are, 

 next to the clouds themselves, the greatest obstacle to good telescopic 

 vision of the heavenly bodies. The results with regard to the 

 clouds were equally satisfactory, for ^ths of the whole were found 

 to be under the level of .5000 feet. 



"On the Phenomenon of Relief of the Image formed on the 

 Ground Glass of the Camera Obscura." By A. Claudet, Esq., F.R.S. 

 The author having observed that the image formed on the 

 ground glass of tlie camera obscura appears as much in relief as 

 the natural object when seen with the two eyes, has endeavoured 

 to discover the cause of that phenomenon, and his experiments and 

 researches have disclosed the singular and unexpected fact, that 

 although only one image seems depicted on the ground glass, still 

 each eye perceives a different image; that in reahty there exist on 

 the ground glass two images, the one visible only to the right eye, 

 and the other visible only to the left eye. Tiiat the image seen by 

 the right eye is the representation of the object refracted l)y the left 

 bide of the lens, and the image seen by the left eye is the reprcscn- 



