170 PHILOSOPHICAL TRANSACTIONS. [aNNO 1715. 



standing waters as perpetually receive rivers running into them, and have no 

 exit or evacuation. 



The number of these lakes, in the known parts of the world, is exceedingly 

 small, and indeed on inquiry I cannot be certain there are in all any more than 

 4 or 5, viz. Ist. The Caspian Sea; 2dly,The Mare Mortuum or Lacus Asphal- 

 tites ; 3dly, The lake on which stands the city of Mexico ; and 4thly, The 

 lake of Titicaca in Peru, which by a channel of about 50 leagues communicates 

 with a 5th and smaller, called the lake of Paria, neither of which have any 

 other exit. Of these, the Caspian, which is by much the greatest, is reported 

 to be somewhat less salt than the ocean. The Lacus Asphaltites is so exceed- 

 ingly salt, that its waters seem fully sated, or scarcely capable to dissolve any 

 more ; whence in summer-time its banks are incrustated with great quantities 

 of dry salt, of somewhat a more pungent nature than the marine, as having a 

 relish of sal ammoniac; as I was informed by a curious gentleman who was on 

 the place. 



The lake of Mexico, properly speaking, is two lakes, divided by the cause- 

 ways that leads to the city, which is built in islands in the midst of the lake, 

 undoubtedly for its security; after the idea, probably which its first founders 

 borrowed from their beavers, who build their houses on dams they make in the 

 rivers after that manner. Now that part of the lake which is to the north- 

 ward of the town and causeways, receives a river of a considerable magnitude, 

 which being somewhat higher than the other, does with a small fall exonerate 

 itself in the southern part, which is lower. Of these the lower is found 

 to be salt, but to what degree I cannot yet learn; though the upper be almost 

 fresh. 



And the lake of Titicaca, being nearly 80 leagues in circumference, and 

 receiving several considerable fresh rivers, has its waters, by the testimony of 

 Herrera and Acosta, so brackish as not to be potable, though not fully so salt 

 as that of the ocean; and the like they affirm of that of Paria, into which the 

 lake of Titicaca does in part exonerate itself, and which I doubt not will be 

 found much Salter than it, if it were inquired into. 



Now 1 conceive that as all these lakes receive rivers, and have no exit or 

 discharge, so it will be necessary that their waters rise and cover the land, until 

 such time as their surfaces are sufficiently extended, so as to exhale in vapour 

 that water which is poured in by the rivers ; and consequently that lakes must 

 be larger or smaller, according to the quantity of the fresh they receive. But 

 the vapours thus exhaled are perfectly fresh ; so that the saline particles brought 

 in by the rivers remain behind, while the fresh evaporates; and hence it is evi- 



