ON ATMOSPHERIC ELECTRICITY AT MADEIRA. 65 



in Portuguese ' l'Este,' which blows with great force, striking in its in- 

 tegrity in a curious manner certain districts alone. 



The wind appears to be generated in the sandy tract of the Great 

 Sahara, and also perhaps beyond in districts extending far into Asia. 

 The heated air of those burning plains ascends tumultuously and pursues 

 a course more or less easterly across the Atlantic. Far above the surface 

 of the water it can imbibe no moisture, and after its descent has become 

 possible by a partial loss of heat it strikes upon the surface of Madeira, 

 depositing sand, locusts, birds, and other evidence of its distant origin, and 

 for a while the mid-day climate of the Great Desert is felt 400 miles away 

 from Africa, in the middle of the Atlantic. The dryness of this wind is 

 wonderful ; it will, in its greedy power of evaporation, separate the dry 

 and wet bulbs of Mason's hygrometer 25° or more, and in a temperature 

 of 80 F. the dew-point is below the freezing point. All clouds disappear, 

 and the sun shines hazily in a sky which exchanges its ordinary deep blue 

 for a semi-transparent colour of light grey. 



The electrical quality of this wind is simply a blank. I have been 

 unable during four favourable opportunities for observing it to detect any 

 registerable amount, either positive or negative ; but I can see under a 

 high magnifying power an irregular swaying to and fro of the needle 

 similar in chai-acter to those given by a broken submerged cable. Pro- 

 bably at its origin, and especially if it takes up much sand, the wind is 

 resinously charged ; but it will be interesting to determine whether an 

 intensely dry wind can be strongly electrified or electrified at all. 



In the neighbourhood of strong l'Este winds I have also made a few 

 observations on some curiously rounded clouds which hang with singular 

 immobility over deep mountain gorges, although tossed and tumbled by 

 strong wind on their upper surfaces. 



I have some evidence to show that both their power and quietness 

 relate to their somewhat high electrical charge, and it is probable that we 

 shall find by-and-by in a more general way that the form of clouds de- 

 pends very much on the influence of neighbouring electrified masses, in a 

 manner nearly related to the experiments of Lord Rayleigh on fountain- 

 jets. But these cloud observations are both difficult and somewhat 

 dangerous. If any one should be tempted to fly a kite with a wet cord 

 and a metallic conductor in its tail down into one of these mountain 

 clouds, he should place his electrometer upon the ground or else have a 

 long trailing copper chain attached to the brasswork. The umbrella, too, 

 must be kept low. If these precautions are neglected a very painful 

 shock will probably be felt, which may cause the observer to drop the 

 instrument. 



The very meagreness of this Report is enough to show the necessity 

 for multiplying electrometric observations. I would only ask, Has the 

 electrometer yet any share in determining our weather forecasts, or is elec- 

 tricity thought of in the relations of meteorology to the public health ? 

 I fear not. 



The fascinating little instrument is my constant companion and the 

 solace of many a leisure moment. It has been taken to the north and 

 south of this country, and has twice crossed the Atlantic with me. In- 

 deed, it never failed to answer every question certainly and sensitively 

 until I attempted last Sunday to take it to St. Paul's in London to take 

 an observation under the dome. Then the pumice-stone broke, and poured 

 its corrosive fluid upon the brasswork. 

 1879. F 



