.186 LIGHT SCIENCE FOR LEISURE HOURS. 



can here afford. Those readers who may wish to 

 understand the origin of the law of cyclonic rotation 

 should study Herschel's interesting work on Meteor- 

 ology. 



The suddenness with which a true tornado works 

 destruction was strikingly exemplified in the wreck of 

 the steamship " San Francisco." She was assailed by 

 an extra tropical tornado when about 300 miles from 

 Sandy Hook, on December 24, 1853. In a few mo- 

 ments she was a complete wreck ! The wide range 

 of a tornado's destructiveness is shown by this, that 

 Colonel Reid examined one along whose track no less 

 than 110 ships were wrecked, crippled, or dismasted. 



(From Temple JBar, December, 1867.) 



VESUVIUS. 



THE eruption in progress, as we write, from Mount 

 Vesuvius, and the numerous and violent eruptions 

 from this mountain during the last two centuries, seem 

 to afford an answer to those who think there are traces 

 of a gradually diminishing activity in the earth's inter- 

 nal forces. That such a diminution is taking place, we 

 may admit ; but that its rate of progress is perceptible 

 that we can point to a time within the historical 

 epoch, nay even within the limits of geological evi- 

 dence, at which the earth's internal forces were cer- 



