544 PHILOSOPHICAL TRANSACTIONS. [aNNO J 762. 



sertatio, &c. a J. A. Braunio^ Academics Scientiarum MembrOj &c. By 

 Wm. rVatson, M. /)., R.S.S. p. 156. 



Very early last year, we were informed, says Dr. W., that at Petersburg, by 

 the means of artificial cold, the mercury in thermometers had been condensed to 

 so great a degree as to become perfectly fixed and solid ; but as this information 

 was received only in a loose way from the public gazettes, the opinions of philo- 

 sophers here were suspended, in regard to their giving credit to this very extra- 

 ordinary phenomenon, till the truth of it could be sufficiently authenticated. 

 This has lately been done by professor Braun, who first made the experiments, 

 and who presented an account of them to the Royal Academy at Petersburg. 



Professor Braun observes, that every age has its inventions, and that the dis- 

 covery of some things seem to be reserved for particular persons. To this, the 

 history of sciences in all ages, more particularly of the late and the present, bears 

 witness sufficiently, by the invention of the air-pump, barometers, thermometers, 

 optical instruments, electricity, more particularly the natural, artificial magnets, 

 phosphorus, the discovery of the aberration of light, and of many other things 

 in natural philosophy. He does not know whether the congelation of mercury, 

 which it was his good fortune to discover, may not be ranged among these: for 

 who did not consider quicksilver as a body which would preserve its fluidity in 

 every degree of cold? Neither was the fact otherwise, if this is understood of 

 natural cold, such as it has been found in any part of the globe hitherto disco- 

 vered. But if it should happen that the natural cold should ever be so intense 

 as artificial cold has been found to be, the whole globe would have a different 

 face, as men, animals, and plants, would certainly be destroyed. He hinted 

 some time since, in a dissertation on the degrees of heat which certain liquors 

 and certain fluids would bear before they boiled, and the degrees of cold thev 

 respectively bore, before they were converted into ice, that there was a suspicion, 

 that the mercury in some of the barometers and thermometers made use of for 

 experiments in Siberia, had been frozen ; but since that in greater degrees of cx)ld, 

 the mercury continued fluid in other barometers and thermometers, the immo- 

 bility and hardness observed in some of these instruments was attributed more 

 probably to the lead of the bismuth, with which the mercury, had been adul- 

 terated, and was not considered as a real freezing of the mercury, but this has 

 been since put out of all doubt, since it is certain, that pure mercury would not 

 freeze under such small degrees of cold, great as they were for natural cold. 

 The experiments which the Professor made, in order to congeal mercury, demon- 

 strate this most evidently, besides which they exhibit new phenomena. 



There happened at Petersburgh, on the 14th of December 1759, a very great 

 frost, equal, if not more intense than any which had been observed there : for 

 between g and 10 o'clock in the morning, Delisle's thermometer stood at 205; 



