30 
of the atmosphere near to the discharging orifice. This 
phenomenon was first observed on a large scale by Mr. 
Kichard Roberts in the year 1824 and is described in a 
paper read before this Society in 1828.^ Roberts noticed 
that, when a valve was placed over an aperture in a pipe 
used for regulating a strong blast of air for blowing a fur- 
nace, 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 aii*. These experiments were repeated, and 
extended, by Mr. Peter Ewart to similar effects produced by 
the discharge of steam through various apertures. Some of 
these experiments were described before this Society, and 
were afterwards published in the Philosophical Magazine in 
1829.*!' The degree of rarefaction produced by the discharge 
of air and high pressure steam was carefully measured by 
Ewart by means of gauges inserted in different parts of the 
jet. He also noticed the sudden fall of temperature from 
292° to 189° F. in the rarefied part of the jet when steam 
of 58 lbs. pressure was discharged into the atmosphere. 
Sir William Armstrong, also, in his experiments on 
Hydro-electricity in the year 1842,^ described a singular 
effect of a jet of steam by which a hollow globe made of 
thin brass, from two to three inches in diameter, remained 
suspended in a jet of high pressure steam issuing from an 
orifice, and when the ball was pulled on one side by means 
of a string, a very palpable force was found requisite to 
draw it out of the jet. 
* Memoirs of tlie Lit. and PM. Society, 2 Series, vol. V., p. 208. 
f Experiments and Observations on some of the Phenomena attending 
the sudden expansion of compressed elastic Fluids. 
J On the Efficacy of Steam as a Means of producing Electricity, and 
on a Curious Action of a Jet of Steam upon a Ball. — Phil. Mag. S. 3. 
Vol. XXII., p. 1. 
