Eruption of Etna* — Petrified Tortoise. 501 



which prevents the alidada from going from one extremity 

 . of this arc to the other, without describing precisely an arc 

 of 180 degrees. In this way the circle i3 in the vertical of 

 the star; and in order to find it, we have only to give to the 

 circle or to the object glass a vertical motion ; but this me- 

 thod would still be insufficient if we had to observe a star by 

 day light, for in this case we might pass far above it without 

 perceiving it. 



If the siar has a perceptible azimuth motion in order to 

 bring it to the centre of the glass, we shall be under the ne- 

 cessity of slackening the screw, in order to displace a little 

 the subsidiary arc : this attention will neither be long nor 

 troublesome. 



This subsidiary arc requires a small change in the form of 

 the alidada; but without in the least changing this form, a 

 simple trace with the crayon upon the azimuth circle, or 

 rather a small spring which should drop in order to allow 

 the alidada to pass, and which should rise when it has passed, 

 would be sufficient for bringing it either to the same posi- 

 tion or to a different position of ISO degrees in azimuth. 



[To be continued.] 



LXXXIX. Intelligence and Miscellaneous Articles. 



ERUPTION O* ETNA. 



feiciLY, April 12, 1S09- — " Mount Etna burst out on the 

 26th or 27th ult. in a most tremendous manner. The first 

 great eruption was from the very top. Twelve new craters 

 opened shortly afterwards, about half way down the moun- 

 tain, and have continued to throw out rivers of burning lava 

 ever since. Several estates have been covered with the lava 

 30 or 40 feet deep. During the first three or four nights, it 

 was seen very distinctly from this place, and a very large river 

 of red hot lava running down from the crater." 



PETRIFIED TORTOISE. 



As some men were lately digging in Swanage rocks, on 

 the island of Purbeck, a petrified land tortoise was discovered, 

 seventy feet deep from the surface, in the highest state of 



perfection j 



