VOL. LXVI.] PHILOSOPHICAL TKANSACTIONS. 69 



wells, from 20 to 60 or more feet in depth ; nor are there any marshes near 

 either town, or indeed in this part of the island. The castle of St. Philip stands, 

 or rather is cut out of the solid rock, on a promontory, -§- of which are washed 

 by the sea, and is open to the sea winds from f of the compass. As there is no 

 tide, there is no slimy shore, which might send forth putrid vapours at low water; 

 and if there were a tide, our shore is one continued rock, on which there is not 

 any putrescent substance. Indeed the rocks are so free from filth, that after a 

 strong wind has raised the seawater, and carried it into cavities hollowed in the 

 rock by storms, it dries there into pure white salt. 



During the hot weather in July, August, and September, our unhealthy sea- 

 son, the air is daily ventilated, either by general winds, which pass freely over 

 the island, or by sea breezes. The air over the land being rarefied by the 

 reflected rays of the sun, and by being in contact with the heale<l earth, neces- 

 sarily makes room for the cooler and denser air in contact with the cooler sea- 

 water. Whence, in such a situation, shall we seek for the causes of tertianas, 

 so called here, and so much dreaded during the hot months? Two causes seem 

 to offer themselves ; one very obvious, the other rather more remote. The 

 southerly winds are much complained of here, as occasioning a general lassitude, 

 and as bringing with them noxious efHuvia from Africa; but whoever considers 

 the distance between this island and Africa, will scarcely believe, that the air can 

 carry with it so far any other quality than the warmth attending the season of the 

 year. Gibraltar, nearer Africa, and more southerly than we are, is not subject 

 to tertians, nor are some places even in this island. The causes therefore must 

 be sought for on the spot. In a situation, such as above described, shade and a 

 plentiful supply of fresh succulent culinary plants must be very desirable. On so 

 dry a rock, an artificial supply of moisture must become necessary, especially in 

 a country where there is seldom rain from May to October. It is not an easy 

 matter to keep a due mean in the use of whatever experience shows to be neces- 

 sary. If a little does good, we are apt to conclude that a great deal will do more 

 good: thus, I think, it fares with us in regard to the use of water in our gardens. 

 In order to have a garden, it is necessary here to have a draw-well. The drawing 

 of water is the labour of an ass; and, as the labour is not hard, the beast is 

 kept at it pretty constantly, and thus plenty of water is drawn up. As the water 

 is hard, and is much colder than the temperature of the air, it is kept in cisterns 

 for some time, exposed to the sun, till it acquires the temperature of the air, 

 and thus becomes more friendly to vegetation than if used immediately on being 

 drawn up. Having thus obtained plenty of water, they bestow it most copiously 

 on their gardens. Suppose yourself landed at St. Philip's in this season of the 

 year, on a dry, parched rock, and that you were told, that the rock was uni- 

 formly the same all the way to Mahon, a distance of 2 miles, and that you were 



