460 



SCIENCE 



[N. S. Vol. XXXI. No. 795 



river waters is perhaps the most important 

 means now available for an estimate of the 

 antiquity of the stratified rocks, because it is 

 the simplest and least open to question. To 

 my thinking the fact that his train of reason- 

 ing coincided with that of the great astron- 

 omer only adds to the credit due Mr. Joly. 



A great amount of work has been done of 

 late years on the composition of river waters, 

 much of it incited by Mr. Joly's memoir and 

 undertaken with the purpose of improving the 

 data for such a determination of the age of 

 the ocean. Within a few months it will be 

 practicable to make known the results of a 

 revised estimate founded upon data far more 

 ample than those at the disposition of Mr. 

 Joly eleven years ago. Mr. F. W. Clarke is 

 now engaged in preparing this estimate. 



The subjoined extracts from Halley's paper' 

 can not but interest all lovers of natural sci- 

 ence. 



On the Cause of the Saltness of the Ocean, and 

 of the Several Lakes that emit no Rivers; with 

 a Proposal, by means thereof, to discover the 

 Age of the World. 



There have been many attempts made, and pro- 

 posals offered, to ascertain from the appearances 

 of nature, what may have been the antiquity of 

 this globe of earth; on which, by the evidence of 

 sacred writ, mankind has dwelt about 6,000 years ; 

 or according to the Septuagint above 7,000. . . . 

 This inquiry seeming to me well to deserve con- 

 sideration, and worthy the thoughts of the Royal 

 Society, I shall take leave to propose an expedient 

 for determining the age of the world by a medium, 

 as I take it, wholly new, and which in my opinion 

 seems to promise success, though the event can 

 not be judged of till after a long period of time; 

 submitting the same to their better judgment. 

 What suggested this notion was an observation 

 I had made, that all the lakes in the world, prop- 

 erly so called, are found to be salt, some more 

 some less than the ocean, which in the present 

 case may also be esteemed a lake; since by that 

 term I mean such standing waters as perpetually 

 receive rivers running into them, and have no exit 

 or evacuation. . . . 



Now I 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 suffi- 



'Phil. Trans., Vol. 29, 1715, p. 296. 



ciently extended, so as to exhale in vapour that 

 water which is poured in by the rivers; and con- 

 sequently 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 evident that the salt in the lakes 

 will be continually augmented, and the water 

 grow Salter and Salter. . . . 



Now if this be the true reason of the saltness 

 of these lakes, it is not improbable but that the 

 Ocean itself is become salt from the same cause, 

 and we are thereby furnished with an argument 

 for estimating the duration of all things, from an 

 observation of the increment of saltness in their 

 waters. For if it be observed what quantity of 

 salt is at present contained in a certain weight 

 of the water, of the Caspian Sea, for example, 

 taken at a certain place, in the driest weather; 

 and after some centuries of years the same weight 

 of water, taken in the same place, and under the 

 same circumstances, be found to contain a sen- 

 sibly greater quantity of salt than at the time of 

 the first experiment, we may by the rule of pro- 

 portion, make an estimate of the whole time 

 wherein the water would acquire its present 

 degree of saltness. 



And this argument would be the more con- 

 clusive, if by a like experiment a similar increase 

 in the saltness of the Ocean should be observed: 

 for that, after the same manner as aforesaid, 

 receives innumerable rivers, all which deposit 

 their saline particles therein; and are again sup- 

 plied, as I have elsewhere showed, by the vapours 

 of the Ocean, which rise from it in atoms of pure 

 water, without the least admixture of salt. But 

 the rivers in their long passage over the earth 

 imbibe some of its saline particles, though in so 

 small a quantity as not to be perceived, unless in 

 these their depositories after a long tract of time. 

 And if, on repeating the experiment, after another 

 equal number of ages, it shall be found that the 

 saltness is further increased with the same incre- 

 ment as before, then what is now proposed as 

 hypothetical, would appear little less than demon- 

 strative. But since this argument can be of no 

 use to ourselves, it requiring very great intervals 

 of time to come to our conclusion, it were to be 

 wished that the ancient Greek and Latin authors 

 had delivered down to us the degree of the salt- 

 ness of the sea, as it was about 2000 years ago: 

 for then it can not be doubted but that the dif- 

 ference between what is now found and what then 



