WITH WHICH AIR RUSHES INTO A VACUUM. 159 



all the pressures from 120 lb. to 40 lb., as shown in the 

 Table. Hence it appeared to me at the commencement of 

 this investigation, that the theoretic and experimental 

 velocities with which air rushes into a vacuum were 

 rigorously exact. The anomalous and apparent increase 

 in the velocities from 40 lb. to 10 lb., however, led me to 

 suspect that the atmosphere in some manner affected the 

 results, and induced me to make the discharge into a 

 vacuum with the results shown in Table I. 



That the phenomenal rate of discharge which I have 

 described should not hitherto have manifested itself in 

 some form, or be associated with some facts explanatory 

 of it, would indeed be surprising considering the varied 

 circumstances in which the discharge of elastic fluids 

 comes into play. Hence, it has long been known that a 

 jet of air issuing from an aperture in a vessel produces a 

 rarefaction of the atmosphere near to the discharging 

 orifice. This phenomenon was first observed on a large 

 scale by Mr. Eichard Roberts in the year 1824, and is 

 described in a paper read before this Society in 1828"^, 

 Koberts noticed that when a valve was placed over an 

 aperture in a pipe used for regulating a strong blast of 

 air for blowing a furnace, the valve, instead of being blown 

 off by the force of the blast, remained a short distance 

 from the aperture, and required considerable force of the 

 hand to remove it to a further distance. Subsequent 

 experiments showed that the adhesion of the valve was 

 caused by the partial vacuum formed between the valve 

 and its seating by the expansion of the issuing air. These 

 experiments were repeated and extended by Mr. Peter 

 Ewart to similar effects produced by the discharge of steam 



* Memoirs of the Literary and Pliilosopliical Society, 2nd series, vol. v. 

 p. 208. 



