VOL, LXVI.] I'HILOSOPHICAL TRANSACTIONS. 117 



lowest state of the thermometer was at 9°, that is, 23° below the freezing point, 

 being 3-t-° below that of the remarkable frost in the year 1739- Having placed 

 on the garden wall, half an ounce of each of the following liquors in a cup, viz. 

 lemon-juice, vinegar, and red-port wine, in that state of the thermometer he 

 found them all perfectly congealed. 



Being desirous to see the effect of a high degree of artificial, added to the 

 natural cold that now prevailed, the thermometer was immersed into a frigorific 

 mixture ; but though it sunk the quicksilver in a few seconds, into the bulb of 

 the thermometer, yet the result was by no means adequate to that of the experi- 

 ment of Professor Braun at Petersburg : for though the quicksilver in the ther- 

 mometer, and that in the phial, contracted a film on the top, yet it remained 

 quite fluid below. 



Jan. 3 1 st to Feb. 1 st, the barometer at 2Q ; the thermometer only at ] 6°, 

 that is, 16° below the point of congelation ; the atmosphere serene and pleasant. 

 Feb. 2d, wind s. ; barometer 29^ ; a warm, misty morning, succeeded by a 

 pleasant, spring-like day, ushered in a very mild and agreeable thaw, the ther- 

 mometer from 9° being got up to 40° ; so great was the change of temperature 

 in so short a space of time ! And it seems worthy of observation, that the epi- 

 demic cold, which had prevailed universally during the preceding mild season, 

 suddenly disappeared in the late intense frost ; but now began to re-appear, to- 

 gether with rheumatic affections and other diseases of the former period. 



XLI. Account of the Magnetical Machine contrived by the late Dr. Goivin 

 Knight, F. R. S., and presented to the R. S. By Jahn Fothergill, M. D., 

 F.R.S. p. 591. 



Dr. F. being left executor to Dr. Knight, a very extraordinary magnetic ma- 

 chine of his contrivance, and which had cost him much labour and expence, 

 came into Dr. F.'s possession. This machine, which may be observed to consist 

 of 2 parts, is by no means so strongly magnetical as it was at the doctor's decease. 

 Not long after this event, it was necessary to remove this apparatus from his 

 apartments in the British Museum. One of these parts was fixed up in the 

 Museum, the other was left at the lodgings of J. H. De Magellan, for the pur- 

 pose of some experiments, and also for impregnating strongly the needles of sea- 

 compasses. Here it was accidentally destroyed by fire, and the parts it consisted 

 of rendered almost wholly useless. A new one was however made, and impregi^ 

 nated with the magnetical power, by the ingenious gentleman abovementioned, 

 according to the method of Dr. Knight. It has acquired a considerable degree 

 of magnetic force, by being placed in the polar line with the other part of this 

 machine that was unhurt, and where in time it willj perhaps, acquire a consider- 

 able degree of magnetic energy. 



