25 



every year the frequency of earthquakes causes 

 more crevices in the soil ; but also because it 

 is now less furnished with wood than it was at 

 the time of the conquest. 



I arose during the night, to determine the la- 

 titude of the place by the passage of Fomalhaut 

 over the meridian. The observation was lost, 

 owing to the time which I employed in taking 

 the level of the artificial horizon. It is the great 

 inconvenience of reflecting instruments, when, 

 on account of the mobility of the fluids, we do 

 not use horizons of mercury, of amalgam, or of 

 oil, but those flat glasses, which have been in- 

 troduced by Mr. von Zach. It was midnight, 

 and I was benumbed with cold, as were also 

 our guides ; yet the thermometer kept at 19* 7° *. 

 At Cumana I have never seen it sink below 21°; 

 but then the house in which we dwelt on the 

 Impossible was 258 toises above the level of the 

 sea. At the Casa de la Polvora I determined 

 the dip of the magnetic needle, which was 

 42*5° The number of oscillations correspon- 

 dent to 10' of time was 233. The intenity of 

 the magnetic forces had consequently augment- 

 ed from the coast to the mountain, perhaps 

 from the influence of some ferruginous matter, 

 :tf&yi '»rfi-%>- ho?j;*)3 "'Hxn. ill M ti^itw&tti 



* 15*5° Reaumur's thermometer. 



t The magnetic dip is always measured, in this work, ac- 

 cording to the centesimal division, if the contrary be not ex- 

 pressly mentioned. 



