CHAPTER I.— THE OBSEEVATORIES OF EUROPE. 



The Teneriffe Experiment (1856). 



Professor C. Piazzi-Smyth, late Royal Astronomer for Scotland, 

 deserves the lasting gratitude of practical astronomers for his under- 

 taking of the Teneriffe experiment in the year 1856. The question of 

 " how much astronomical observation can be benefited by eliminating 

 the lower part of the atmosphere " was for the first time plainly put 

 and partially solved. In two works, one the scientific report of his 

 expedition to the Royal Society of London,* the other more popular, f 

 the question was stated in the plainest manner, and a partial conclusion 

 was reached. I refer to the original works, just cited, for the history 

 of the idea, which appears to have been entirely original with Professor 

 Smyth, and only remark in passing that the expedition to Teneriffe 

 was undertaken by the aid of a government grant, with the benefit of 

 the advice of several distinguished astronomers, among them Sir 

 George Airy and Sir John Herschel, and that it was greatly aided by 

 Robert Stephenson, the Engineer of the Britannia Tubular Bridge. So 

 much should be said in even the shortest notice of the expedition. 



The summer of 1856 was spent at Teneriffe, and the instruments 

 were set up at two stations, Guajara (8903 feet) and Alta Yista (10,702 

 feet). The summit (12,198 feet) was also visited. A little over two 

 months was devoted to the work. A telescope of 7^ inches in aper- | 

 ture was employed. The conclusions of Professor Smyth were briefly " 

 as follows : 



"With increased altitude (comparison of Teneriffe with Edinburgh) i 

 the transpca-ency of the air was much improved (as was expected) ; and I 

 its steadiness also. (Teneriffe is a small island in the trade-wind belt, [* 

 and the surrounding ocean should tend to equalize temperature and to 

 produce good definition.) 



The definition appeared to be equally good over all parts of the 

 sky, and for the whole night, except shortly after sunset. During the 

 daytime " the sun was seldom well defined." The blueness of the sky, 

 even at the highest station, was in no wise remarkable. A " glare, 



* Philosophical Transactions, yoI. cxlviii, 1858, p. 465. 

 •}• Teneriffe, — An Astronomer's Experiment. 



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