Chap. 21.] WHOLESOMENESS OF WATEKS. 483 



salubrious by its current and its continuous agitation. Hence it 

 is that I am much surprised that persons should be found to 

 set so high a value as they do, upon cistern water. These last 

 give as their reason, however, that rain-water must be the 

 lightest water of all, seeing that it has been able to rise 85 aloft 

 and remain suspended in the air. Hence it is, too, that they 

 prefer snow-water to rain-water, and ice, again, to snow, as 

 being water subtilized to the highest possible degree ; on the 

 ground that snow-water and ice- water must be lighter than 

 ordinary water, and ice, of necessity, considerably lighter. It 

 is for the general interest, however, of mankind, that these 

 notions should be refuted. For, in the first place, this com- 

 parative lightness which they speak of, could hardly be ascer- 

 tained in any other way than by the sensation, there being 

 pretty nearly no difference at all in weight between the kinds of 

 water. !Nor yet, in the case of rain-water, is it any proof of 

 its lightness that it has made its way upwards into the air, 

 seeing that stones, 89 it is quite evident, do the same : and then, 

 besides, this water, while falling, must of necessity become 

 tainted with the vapours which rise from the earth ; a circum- 

 stance owing to which it is, that such numerous impurities 90 

 are to be detected in rain-water, and that it ferments 91 with 

 such extreme rapidity. 



I am, surprised, too, that snow 92 and ice should be regarded 

 as the most subtilized states of this element, in juxtaposition 

 with the proofs supplied us by hail, the water of which, it is 

 generally agreed, is the most pernicious of all to drink. And 

 then, besides, there are not a few among the medical men 

 themselves, who assert that the use of ice-water and snow- 

 water is highly injurious, from the circumstance that all the 

 more refined parts thereof have been expelled by congelation. 

 At all events, it is a well-ascertained fact that the volume of 

 every liquid is diminished by congelation ; as also that exces- 



88 Rain-water really is the lightest, but the reason here given is frivolous, 

 for it does not ascend as water, but as vapour. 



89 See B. ii. c. 38. Before venturing on this argument, he should have 

 been certain as to the circumstances under which aerolites are generated, a 

 question which still remains hidden in mystery. 



* Ajasson remarks that this is only the case in the water of heavy falls 

 of rain after long drought. 91 " Calefiat." 



32 Snow-water is pernicious in a very high degree, being the fruitful 

 source of goitre and cretinism. 



II 2 



