142 SECTION PHYSICS. 



is thrown with the utmost velocity, at the moment of freezing. So 

 that in quoting the terms by which they signified the different con- 

 ditions which they observed, and in telling you what they meant to 

 define by each one of them I have already informed you of the im- 

 portant observations which they succeeded in making. They proved 

 the salto dell' immersione, not only by thrusting the ball into ice, 

 but into hot water. The quiete corresponds to our maximum of 

 density of water, which was indicated in their thermometers by 119. 

 Sollevamento is the expansion which the water undergoes from 4 

 down to the point at which it freezes. Then the word salto (leap, 

 jump) shows us how the phenomenon of freezing takes place rapidly ; 

 in fact the academicians well observe the almost instantaneous freezing 

 of water in certain cases namely, when left to itself, its temperature 

 descends to below o, and being then shaken (the ball having been 

 taken from the snow, as they were accustomed to do, to see the salto 

 del? agghiactiamento) all of a sudden the whole of its mass became solid. 

 And conditions similar to these they observed in spring water, and in 

 water distilled from various substances, in wines, in vinegar, in spirits of 

 vitriol, in oil, in which, however, they found no rarefaction, so that 

 frozen oil sinks to the bottom of fluid oil, and in brandy, which con- 

 tracts itself regularly but does not freeze. As to natural freezing it 

 was so minutely observed and described that it fills one with astonish- 

 ment and admiration. They proved that ice produced in vacuo is 

 more compact and weighs more than in the air ; and that when water 

 freezes slowly in a glass it makes first of all a crust, which, being 

 pressed, in some place or other, by the expansion of the remainder of 

 the water affected little by little by the cold, breaks open, so that from 

 the aperture there issues a certain amount of water, which, freezing in 

 its turn, renders the surface of the ice convex ; and sometimes if the 

 cold be intense, wrinkled, or rather forms an excrescence of ice, which 

 can even reach the height of a finger. And this observation recalls to 

 my mind the experiments of the illustrious Gorini, and his theory on 

 the origin of volcanoes and mountains. But if the crust be too thick 

 and the expansion underneath be not able to break it, it generally 

 happens that the vessel bursts. Then they pointed out the difference 

 between the ice of ordinary water, of distilled water, of sea water, and 

 the congealing action of common salt, and of the more efficacious salts 



