TRANSACTIONS OF THE SECTIONS. 25 



Port Louis some of them were condemned, and some detained for two or three 

 months undero-oing repairs. The loss on that single occasion must have amounted 

 to at least £60,000, and there is not the slightest doubt that it would have been 

 avoided if the vessels had kept back for a day or two, and not run headlong into 

 the storm. In the hurricane season, in those latitudes, with the wind anywhere 

 between north and south, through the west, the weather squally and threatening, 

 and the barometer falUng, a vessel should not press too much to the southward. 

 B}^ attention to this rule the storm will be avoided. 



Experience has proved that the existence of a gale belonging to any one ot the 

 three classes above described is indicated at Mam-itius by the barometer, winds, 

 and weather, even when the distance is very considerable. A trade-wind gale is 

 preceded by a high and rising barometer, and by the setting in of the wind at 

 southward, generally with a clear sky. On the other hand, the barometer at Mau- 

 ritius always falls during a gale belonging to either of the other two classes. As 

 a general rule, if the barometer fall steadily for three or four days to the extent of 

 even one-tenth of an inch below its height for the season, it may be inferred either 

 that a tropical gale exists on the equatorial borders of the trade-wind, or an extra- 

 tropical one on its polar borders ; and the direction and veering of the wind, and 

 the character of the clouds, will determine in which of these directions the 

 disturbance is taking place. At the setting in of a tropical gale awaj^ to the north- 

 ward or N.E., the trade-wind at Mauritius is drawn towards the locality of dimi- 

 nished pressure, and the barometer falls. When an extra-tropical gale takes place 

 away to the S.W., towards the Cape of Good Hope, the trade-wind is deflected 

 in that direction, so as to form a pai-t of the X.E. winds of the east side of the 

 gale, and in this case also the barometer falls at JMauritius, until the southerly winds 

 of the west side of the gale have begun to exert their influence, as the gale ad- 

 vances to the eastward. The existence of all the heavy gales which have taken 

 place in either direction, for some years back, has been known at Mauritius, and 

 frequently announced in the newspapers at the time. 



On Meteorological Observations at Sea. By F. "VV. Moffat. 

 Communicated by Dr. Moffat. 

 These observations were made for the purpose of ascertaining the quantity of ozone 

 in different degi-ees of latitude and longitude at sea. The observations extend 

 between lat. 53° N. and 39° S., and long. 83° E. and 25° W. The author had ob- 

 served that as the wind veered with increasing readings of the barometer from south 

 points of the compass through west to north, ozone disappeared, and continued 

 absent while the wind was in points between north and east, and that it reap- 

 peared as the wind veered with decreasing readings of the barometer to south 

 points. The disappearance and reappearance of ozone with these conditions were 

 so regular that the changes appeared to be the result of an invariable atmo.spheric 

 law, and the author was induced to examine the law of the rotation of the wind, 

 so clearly developed by Dove, and the results of the examination led him to believe 

 that the polar current is the non-ozoniferous, or that of minimum of ozone, and 

 that the equatorial, or sea-wind, is the ozoniferous, or that of the maximum of 

 ozone. According to the rotation theory, the polar current in the northern he- 

 misphere forms the N.E " trade," and that in the southern hemisphere forms the 

 S.E. " trade," while the equatorials in the northern and southern hemispheres form 

 the upper or returning "trades." These returning "trades" come to the earth's 

 surface in both hemispheres about the 28th degree (the latitude varies with the 

 season), north and south of the equator. The author stated that if his deductions 

 are trustworthy, the N.E. and S.E. "trades" ought to be the minimum of ozone 

 cun-ents, and the returning " trades" the maximum of ozone currents ; that in the 

 northern hemisphere forming the S.W. wind, and the other in the southern hemi- 

 sphere a N.W. wind ; and as these currents consisted of the atmospheres of equa- 

 torial latitudes, the quantity of o^one ought to be at least as gi-eat at the equator 

 as with the returning cun-ents. The author showed by tabulated results that such 

 was the case, and he expressed a belief that were it not for the modifying effects 

 of the trade-winds, ozone would be a constant quantity at sea. 



