240 THE POPULAR SCIENCE MONTHLY. 



mine, excavated also in the tuff. Its height being about 16 feet (above 

 the sea '?), its breadth 12, and its depth about 150, it offers, in its pro- 

 portion of twelve and a half diameters, the greatest contradiction to 

 all other instances of sea-worn homogeneous rock. 



But not only do Cormorant's and Fingal's Cave, each protected by- 

 its breakwater, face the adjacent land and not the open sea, and that 

 land the far-famed Island of lona, center of art and civilization, " dear 

 to Christendom for more than a thousand years," but from the end of 

 this deep cavity, to which a boat may sail in any ordinary weather, the 

 " Dun " or Hill of " Hy " or lona rises against the sky, in the middle 

 of the arc of a few degrees subtended by the grand doorway. Until 

 it is shown that a thousand yards of landlocked, iron-bound coast can 

 be cut and tunneled in utter disregard of every known law of mechan- 

 ical action, the caves in Staffa, on the west coast of Scotland, driven 

 into igneous rock, not modified by local conditions, or in the weak 

 places " of an exposed cliff," can not be classified as merely remarkable 

 instances of caves worn by the sea. Had the learned duke who com- 

 menced his description of lona with these words, " No two objects of 

 interest could be more absolutely dissimilar in kind than the two 

 neighboring islands of Staffa and lona," " mixed Celtic memories with 

 the Phrygian mount," recalled Athos, Tyre, and Carthage, or even the 

 twin Island of Lerins, he might have hesitated to put them in sharp 

 antithesis to say that only an accident of geography could unite their 

 names, or with " the mighty surge " of personal and social authority 

 drowned the faint cry for relief which reached his ears, and declined 

 even to consider the solution here offered of a problem whose com- 

 plex factors he had so forcibly stated. 



-*<> 



THE SPECTEOSCOPE AND TOE WEATHER. 



By C. PIAZZI SMYTH, 



ASTRONOMER ROYAL FOR SCOTLAND. 



WHAT may be done with the spectroscope in the matter of 

 weather is, for the present at least, confined almost entirely to 

 the question of rain as, Will it rain, or will it not ; and, if it will, 

 heavily or lightly ? The manner in which the spectroscope accom- 

 plishes this useful part is by its capacity for showing whether there is 

 more or less than the usual quantity of watery vapor permeating the 

 otherwise dry gases in the upper parts of the atmosphere, this watery 

 vapor not being by any means the visible clouds themselves, but the 

 invisible water-gas out of which they have to be formed, and by 

 means of which, when over-abundant, they obtain their privilege for 

 enacting rain-fall. So that never were wiser words uttered and more 



