THE 



PHILOSOPHICAL TRANSACTIONS 



OF TBE 



ROYAL SOCIETY OF LONDON; 



ABRIDGED. 



Extract of a Letter of M. Huygens, to the jiuthor of the Journal des Savans, 

 of July 25, 1672, attempting to explain the Cause of that odd Phenomenon 

 of the Quicksilver s remaining suspended far above the usual Height in the 

 Torricellian Experiment. N° 86, p. 5027- 



A HE Experiment is briefly this : that a tube, being after the Torricellian 

 way, filled with mercury, and before inversion perfectly purged of air, does, 

 when inverted, remain top full, even to the height of 75 inches. 



M. Huygens, as a probable cause of this strange effect conceives, that besides 

 the pressure of the air, which keeps the mercury suspended at the height of 

 about 27 * inches, and of the truth of which w^e are convinced by a great number 

 of other effects ; there is yet another pressure stronger than that, of a more 

 subtle matter than air, which without difficulty penetrates glass, water, quick- 

 sih^er, and all other bodies which we find impenetrable to air. This pressure, 

 he says, being added to that of the air, is capable of sustaining the 75 inches of 

 mercury, and possibly more, as long as it works only against the lower surface, 

 or against that of the mercury, in which stands the open end of the tube : but as 

 soon as it can work also on the other side, (which happens when striking against 

 the tube, or intromitting into it a small bubble of air, you give way to this 

 matter to begin to act) the pressure of it becomes equal on both sides, so that 

 there is no more but the pressure of the air, which sustains the mercury at the 

 ordinary height of 27 inches. 



If you ask why the quicksilver in the tube of this experiment does not feel 

 the pressure of this matter, even whilst that vessel is yet full ; since M. Huy- 

 gens supposes, that it pierces without difficulty the glass as well as the mercurv 

 &c ? and why the particles of this matter do not join together and begin the 



* French measure, or nearly 29 inches English measure. 

 VOL. II. B 



r r '7 O 



