540 PHILOSOPHICAL TRANSACTIONS. [aNNO I67O. 



and returned to Rome, without making mention of any such danger. Where- 

 fore that country not being unwholesome of its own nature, but from adventi- 

 tious causes, it is probable that those may be removed, as has been proposed by 

 J. Battista Donius in his book De Restituenda Salubritate Agri Romani. 



The cause of the extreme unhealthiness of the air in those parts, is ascribed 

 to the noxious vapours from the stagnant waters and marshes. And the chief 

 means recommended for curing the evil are, draining the low lands, encourag- 

 ing people to settle there, and to till and cultivate the land. 



An Experiment concerning the Progress of Artificial Conglaciation, 

 and the remarkable Accidents therein observed by the Florentine Phi- 

 losophers, and published in their Saggi di Naturali Esperienze. 

 N' 66, p. 2020. 



The first vessel we used (say those eminent academists) for this experiment, 

 was a globe of crystal, whose diameter was -f of a braccio,* with a long straight 

 neck of about a braccio and a half, graduated into small parts. Having filled it 

 with common water up to the sixth part of the neck, we put the globular part 

 into ice and salt, after the usual manner of artificial freezing of liquors, and 

 began very attentively to observe all the motions of the water from its level. It 

 was sufficiently known before, that freezing works in all liquors a contraction ; 

 as also that in the passage, which the water makes from being simply cold, to 

 the leaving of its fluidity, and taking a consistency and hardness by congelation, 

 it not only returns to the bulk it had before it was frozen, but swells to a 

 greater; since we see that vessels, not only of glass but of metal, are forcibly 

 broken thereby. But what might be the limits and period of these various 

 alterations, which the cold works therein, we as yet did not know ; nor is it 

 possible to attain that knowledge in opaque vessels. Therefore, that we might 

 not want that insight, which appeared to be the soul of all these experiments, 

 we had recourse to crystal and glass, hoping that by the transparency of that 

 body we should be informed of the whole progress ; as at every motion which 

 should appear in the water of the neck, we might quickly take the globe out of 

 the ice, and observe the alterations correspondent thereto. But the truth is, 

 that we took more pains than we can express, before we could find out any 

 thing certain touching the periods of these accidents. 



In the first immersion of the globe, as soon as it touched the icy water, there 

 was observed in the water of the glass's neck a small rising, but that sufficiently 



* Near three English inches. 



