VOL. XVI.] PHILOSOPHICAL TRANSACTIONS. 380 



allowances being made for the places where it is broader by those where it is 

 narrower, (and I am sure I guess at the least,) there will be 1 60 square degrees 

 of sea; and consequently, the whole Mediterranean must lose in vapour, in a 

 summer's day, at least 5280 millions of tons. And this quantity of vapour; 

 though very great, is as little as can be concluded from the experiment pro- 

 duced. And yet there remains another cause, which cannot be reduced to 

 rule, I mean the winds, whereby the surface of the water is licked up some- 

 times faster than it exhales by the heat of the sun; as is well known to those 

 who have considered those drying winds which blow sometimes. 



To estimate the quantity of water the Mediterranean sea receives from the 

 rivers that fall into it, is a very hard task, unless we had the opportunity to 

 measure their channels and velocity; and therefore we can only do it by allow- 

 ing more than enough; that is, by assuming these rivers greater than in all 

 probability they are, and then comparing the quantity of water voided by the 

 Thames, with that of those rivers whose water we desire to compute. 



The Mediterranean receives these considerable rivers, the Iberus, the Rhone, 

 the Tiber, the Po, the Danube, the Neister, the Borysthenes, the Tanais, and 

 the Nile, all the rest being of no great note, and their quantity of water incon- 

 siderable. These nine rivers, we will suppose each of them to bring down 10 

 times as much water as the river Thames, not that any of them is so great in 

 reality, but to comprehend with them all the small rivulets that fall into the sea, 

 which otherwise I know not how to allow for. 



To calculate the water of the Thames, I assume that at Kingston bridge, 

 where the flood never reaches, and the water always runs down, the breadth of 

 the channel is 100 yards, and its depth 3, it being reduced to an equality; in 

 both which suppositions I am sure I take with the most. Hence the profile of 

 the water in this place is 300 square yards ; this multiplied by 48 miles, which 

 I allow the water to run in 24 hours, at 2 miles an hour, or 84480 yards, gives 

 25344000 cubic yards of water, to be evacuated every day ; that is, 20300000 

 tons per diem ; and I doubt not but in the excess of my measures of the channel 

 of the river, I have made more than suflicient allowance for the waters of the 

 Brent, the Wandel, the Lea, and Darwent, which are all that are worth notice, 

 that fall into the Thames below Kingston. 



Now if each of the aforesaid 9 rivers yield 10 times as much water as the 

 Thames does, it will follow that each of them yields but 20300000 of tons 

 per diem, and the whole 9 but 1827000000 of tons in a day; which is but 

 little more than 4- of which is proved to be raised in vapour out of the Mediter- 

 ranean in 12 hours time. Now what becomes of this vapour when raised, and 

 how it comes to pass that the current always sets in at the mouth of the 

 Straits of Gibraltar, is intended, with leave, for a farther entertainment of this 



