F 104 ] 



mixture. In two minutes the mercury funk out of the tube 

 quite into the globe. The fcale extends only twenty-five degrees 

 below O of Fahrenheit; wherefore I could not determine how 

 many degrees lower it would have funk on a more extended fcale. 

 In five minutes, fome {lender laminae of ice began to moot from 

 the circumference of the water, and adhered to the glafs. The 

 whole water was not frozen in lefs than an hour, at which time 

 the mercury in the Thermometer rofe to twenty degrees below 



0. Having another mixture of the fame kind ready made, I 

 brilkly removed the tumbler with the ice it contained into the 

 frefh mixture, which, like the former, funk the mercury into 

 the globe. 



" The ice of fea- water is more opaque than that of frem 

 water, when both are naturally congealed. For the elaftic fluid 

 in common water forms bubbles only in the central parts of the 

 water laffc frozen ; but the ice of fea-water confifts of alternate 

 parts of ice and brine ; the denfity of which being unequal, and 

 the matter of them being alio diflimilar, light cannot be freely 

 tranfmitted, but is partly reflected and refracted, according to Sir 



1. Newton's Ideas of light. 



" In the experiment laft-mentioned, the ice was- commonly 

 ■opaque; and when it was expofed to the frefh frigorific mixture, 

 it became like a mafs of mow compreffed, having a fnowy white- 

 nefs and opacity, perfect near the furface, but not perfect to- 

 wards the bottom. 



" The tumbler,with the ice it contained, was kept in this laft- 

 mentioned mixture an hour, when the mercury denoted that no 

 further degree of cold could be given by this mixture. The 

 tumbler was then placed in lnow .until .the next day, to preferve 

 the ice for further obfervation. Notwithftanding the extreme 

 cold to which it had been fo long expofed 3 and the cold medium 



in 



