746 



degrees below zero. The north winds on the 

 eastern coast of Mexico, at Vera-Cruz, (lat. 

 19° 11') often interrupt suddenly the regularity 

 of the horary variations, during 5, 6, and even 

 8 days, and make the mercury oscillate from 

 333 to 341 lines, (difference 18 millimeters). 

 I have stated in another place the importance 

 of which this phenomenon, studied by M. Orta, 

 captain of the port of Vera-Cruz, in all its 

 various modifications, is become for the safety 

 of navigators who would sail in these dan- 

 gerous latitudes. By inspecting the barometer, 

 the proximity of the tempest, its force and 

 duration may be prognosticated with great pro- 

 bability. I saw in the possession of M. Orta, 

 near 28,000 thermometries and barometric ob- 

 servations, made with excellent instruments of 

 Dollond, at the port of Vera-Cruz, from 1791, 

 to 1803, four times a day, at 6 h in the morning, 

 at noon, 4h in the afternoon, and 10 h in the 

 evening. I advised that indefatigable observer 

 to send a mass of materials so valuable, (the 

 most considerable perhaps that was ever col- 

 lected within the tropics, on the same spot), to 

 Europe, to be deposited in the archives of 

 some learned society. It is to be feared that 

 the calamities which the town of Vera-Cruz 

 has recently suffered during the bombard- 

 ment of the Castle of San Juan d'Uloa, may 

 have deprived the scientific world of the 

 labours of M. Orta. 



