262 OBSEEVATIONS ON THE WINDS. 



lightful than the subsequent clear and pure state of the air, creating an 

 apparent regeneration of the animal as well as of the vegetable world. 



Commander E. G. Bourke, E.N., says : — Tornados are met with as far 

 as 10° S., and almost always come from the Eastward, or dead against the 

 prevailing winds : they do not appear to have any rotatory motion, and 

 have scarcely any effect on the barometer ; if they cause any change, it is 

 a slight rise on their approach. This is to be looked for, as they work dead 

 against the usual wind, and the two currents of air seem to meet ; certain 

 it is that the S. W. wind blows till the squall reaches the observer, when a 

 sudden change occurs to the N.E. It appears to me that the cold upper 

 current of air forces its way against and under the exceedingly hot and 

 moist lower one, forcing it upwards, where it is rapidly condensed into 

 angry-looking clouds which fringe these storms, the Tornado being in this 

 way constantly fed with rain and electricity as it progresses. On the 

 approach of a Tornado, the temperature frequently falls 15*^ in 3 or 4 

 minutes, I traced the path of one for 120 miles along the Gulf of Guinea, 

 which travelled that distance in 4 hours, and its course was W.S.W. true. 

 This Tornado I observed on shore at Accra, and by referring to the logs of 

 the men-of-war which were at anchor off other places, I discovered its rate 

 of progression. 



Tornados are most violent and frequent in the neighbourhood of Sierra 

 Leone, and also at the island of Fernando Po : they are most frequent at 

 the commencement and close of the rainy season (June to September), and 

 are most violent at the former period ; they do, however, occur occasion- 

 ally throughout the dry season, but I have never seen one during the rainy 

 season proper. They extend a long distance to seaward, in fact, all over 

 the region of the S. W. Monsoon, but diminish in frequency as the distance 

 from land increases. During the rainy season (June to September), espe- 

 cially in the Gulf of Guinea, the S.W. Monsoon (it then being at its greatest 

 strength) frequently blows home to the coast, obliterating the sea and land 

 breezes. On these occasions the weather is most oppressive, as the night 

 temperature remains very high, the diurnal range being but 3° or 4°. — 

 Journal of the Meteorological Society, vol. iv., 1878, page 26. 



(208.) Captain Henry Toynbee, in his remarks accompanying the 

 Monthly Charts, mentioned in the note on page 136, states as follows : — 

 In April, Tornados occur on the S.W. coast of North Africa. They gene- 

 rally commence with a South-Easterly gust, and then back to the East- 

 ward, sometimes working round until they end at S.W. ; but their action 

 does not seem to be always the same. They occur where the Northerly 

 wind is giving way to the Southerly, or the Southerly to the Northerly, as 

 these winds work their way to the Northward or Southward, so that their 

 season varies with the latitude ; but they may be said to begin on the 

 Southern part of this coast in April, and to work their way Northward 

 during the summer months ; then as the Northerly wind advances to the 

 Southward, they are felt again on the Southern part of the coast in October. 



(209.) Dr. A. Borius, of the French Navy, gives the following account, 

 from his experiences of a great number of Tornados in Senegal :* — 



" Recherches sur le Climat du Seut-gal," par Dr. A. Borius. 



