238 Mr Richard Adie on the Causes which Influence 



the air from the direction of the countries whose temperatures are so 

 much elevated, may be thought to militate against the inference, that 

 their climates are improved by heat from that source ; but the con- 

 tinued stream of air in the region of the trade-winds all round the 

 world, wherever the surface of the earth is uninterrupted by table- 

 lands or mountain ranges, from NE., must have a counterbalancing 

 SW. wind somewhere ; for which reason it has long been held, that 

 the south-west winds of the temperate zone compensate or restore 

 the atmospheric equilibrium which a perpetual NE. trade-wind 

 would disturb. 



Taking, then, the SW. winds as the return currents of air carried 

 towards the equator by a NE. trade-wind, the influence of the heated 

 air of the Sahara should reach Europe by a SW. wind ; then, if we 

 allow that much of the heat received by the air in the desert has 

 assumed a latent form in aqueous vapour during the transit, we should 

 next expect to find that where the aqueous vapour is chiefly con- 

 densed, the isothermal lines tend furthest northward, a supposition 

 which agrees well with the position of the isothermal line for 32° 

 temperature on the coast* of Norway. 



The climate of western Europe may be held to owe its favoured 

 temperatures to two distant sources of heat. The first, and most 

 important, from a tropical sun acting on the air over the greatest 

 desert in the world ; the second from the same tropical sun heating 

 the waters of the Carribbean sea. The action of the sun on ground 

 destitute of vegetation is well known to heat the incumbent air with 

 rapidity ; in dry bright weather the air over a fallow field in this 

 country is seen agitated by the uprising currents of air ; and I have 

 seen a thermometer placed on the soil, and covered with a little 

 powdered dry earth, stapd, on 1st August, at 120° Fahrenheit. In 

 the African desert, there is within a short aerial journey of us, a 

 mass of heated air greater than can be found in any other place of 

 the same magnitude. The space of time required for the transmis- 

 sion of this air to Europe must, I fear, remain a matter of conjecture, 

 the probability is that it may reach the latitude of London in 100 

 hours. The second source of heat, the Carribbean sea, has an area 

 nearly the same as the Sahara, so that there may be an amount of 

 solar influence to transmit to northern regions nearly equal to that 

 from the Sahara. The gulf stream passes for a course of 1800 

 geographical miles along the American coast, bathing the shores of 

 places possessing low temperatures for their latitudes, but which are 

 nevertheless influenced by the gulf stream ; for, receding from the 

 shore inland, the isothermal line tends to the south ; while, for 

 Europe, the gulf stream has to make another journey of 1800 miles, 

 where its influence must be still less than on the American coast, 



* Vide Charts by M. Humboldt and Professor Dove. 



