METEOROLOGY. 477 



nary mean barometric pressm'o from the same som'ce is 26'°.962517, the true 

 mean 26^".962515; the first shows a difference of +0°.004, the second of 

 0.000002 inches. 



It is easy to prove that this difference (J) for a common year is represented 

 by the following equation : 



4380J = 7 {mi-\-ni2-\-i)i5-{-m--\-mQ+iniQ+mi2)—29 m-i—Q (>»4+»?g+"'9+'^''ii) 

 and for a leap year: 



732J = l^ml-\-m^-\-m',+m-, + mc, + nhQ-\-ml^—{m^+mfi-{■mci■^rmn)—^m2 

 where mi m-i m^, etc, are the monthly means corresponding to the first, second, 

 third, etc., month. 



Taking again the case of Caracas as an example, we find a differenee for the 



2.82 

 thermometric means of -y^ ^=^ 0°.0038 as stated above, and for the barometric 



0.0016 

 pieans of ^gg - -= 0.0000022 as before. 



AX ACCOUNT OF A CTCIOXE, JAXl ARY 6 AND 7, 1867, EXCOUXTERED BY THE 

 UMTED STATES STEAMER MONOCACY, WHILE OX HER PASSAGE FROM 

 SIMOX'S BAY TO 3IAIRITIUS, IX THE IXDIAX OCEAX. 



By Nicholas Pike, United States Consul, Port Louis. 



The United States steamer Monocacy, bound from Simon's bay. South Africa, 

 towards Mauritius, met, during the passage to the last-mentioned port, one of 

 those dreaded tornadoes or hurricanes that swept over the vast expanse of the 

 South Indian ocean. Being m^'self on board of the Monocacy, and deeply inter- 

 ested in the science of the laws of storms, I succeeded, by careful observations 

 of barometer and thermometer, by noticing the changes of wind and tempera- 

 ture, and the rising and setting of the storm wave, to ascertain pretty correctly 

 the centre of the hniTicane, and deduce all the aforesaid changes of wind and 

 •weather to the rules laid down b\" Messrs. Piddington and Ecdfield, in their 

 admirable treatise on the law of storms; the otHcers of the vessel kindly supply- 

 ing me with a copy of the log, which, if even not very correct, greatly aided 

 me in tracing the cyclone home to its vortex. 



As my object in writing this is not a description of the storm, but especially 

 facts and dates, and arranging such in taldes to pi'ove the coiTectness of the 

 theory of cyclones, I shall previously insert a short description of the tempest. 

 The whole of our ])assage, since leaving Simon's bay, had been a succession of 

 bad weather, and the few sunny days which we in realitj' had were both to 

 ofiicers and men a veritable blessing; sails were repaired, hammocks and bed- 

 ding aired, clothes dried and mended, and the decks, for the first time quite dry, 

 resounded in every direction with the joyous laughter of the crew, carelessly for- 

 getting the past troubles, living only for the present, regardless for the future. 

 But their joy was of short duration. On the evening of the 6tli of January, the 

 sky became gloomy, dark threatening clouds passed swiftly to the northward, 

 the sea rose fast, and the vessel commenced to roll heavily ; bedding and clothes 

 were quickly taken below, and everything secured for the bad weiither again. 

 The night, from January 6 to 7, fully justified our anticipations ; heavy blasts of 

 wind, rain, and lightning, the rolling of the vessel, the cracking of her timbers, and 

 the thundering noise of a wave breaking under the vessel's counter, made, I may 

 safely say, even the oldest seamen on board uncomfortable, especially as the 

 vessel being new, and her sea-worthiness to all, even to the captain, unkno\TO, we 

 Lad not that confidence in her which her gallant behavior afterwards during the 



