VOL. LXV.] PHILOSOPHICAL TRANSACTIONS. 6l3 



was suggested. As we know from experience, that by disturbing common water, 

 we hasten the beginning of its congelation, or render it incapable of being cooled 

 below 32°, without being congealed ; may not the only difference between 

 it and boiling water, when they are exposed together to a calm frosty air, consist 

 in this circumstance ; that the boiled water is necessarily subjected to the action 

 of a disturbing cause, during the whole time of its exposure, which the other 

 is not ? One effect of boiling water long, is to expel the air which it naturally 

 contains ; as soon as it cools, it begins to attract and absorb air again, till it has 

 recovered its former quantity ; but this probably requires a considerable time. 

 During the whole of this time, the air entering into it must occasion an agita- 

 tion or disturbance in the water, which, though not sensible to the eye, may 

 be very effectual in preventing it to become, in the least, colder than the freez- 

 ing point, without beginning to freeze, in consequence of which, its congelation 

 must begin immediately after it is cooled to that point. When I reflect on this 

 idea, I remember a fact which appears to me to support it strongly. Fahren- 

 heit was the first person who discovered that water, when preserved in tran- 

 quillity, may be cooled some degrees below the freezing point without freezing. 

 He made the discovery while he was endeavouring to obtain ice from water that 

 had been purged of its air : with this intention he had put some water into little 

 glass globes, and having purged it of air, by boiling and the air-pump, he sud- 

 denly sealed up the globes, and then exposed them to the frosty air. He was 

 surprized to find the water remain unfrozen much longer than he expected, 

 when at last he opened some of his globes, in order to apply a thermometer to 

 the water, or otherwise examine what state it was in. The immediate conse- 

 quence of the admission of the air was a sudden congelation, which happened in 

 the water; and in the rest of his globes, a similar production of ice was occa- 

 sioned by shaking them. The inference that may be drawn from these experi- 

 ments of Fahrenheit's, is sufficiently obvious ; it appears to remove all doubt 

 with regard to the above supposition. Before these experiments of Fahrenheit 

 occurred to mymemory, I had planned a few, suggested by the above sup- 

 position, that might have led to the same conclusion ; but the short dura- 

 tion of the frost, for one day only, did not give me time to put them in 

 execution. 



XIV. Experiments on the Dipping- Needle, made by Desire of the R. S. By 



Thomas Hutchins. p. \2Q, 



In these experiments the instrument was placed in 4 several positions, viz. 

 with the index placed east, and then placed west, with the poles of the needle 

 placed one way, and then the same with the poles changed or reversed. In each 



