On the Cause of the Collapse of a Reservoir. 243 
mand the most elevated rooms in our dwelling houses. Hence, had 
the reservoir been burst, it would not have excited surprise; but the 
converse appeared inexplicable. The figure delineated below, will 
convey a correct idea of the reservoir as it appeared when I exam- 
ined it; or subsequently, when a drawing of it was made at the 
Franklin Institute, to which it had been removed, at the instance of 
some of the members of that institution. ; 
A, is a pipe with a stop cock to allow 
the air to escape on first filling the reser- 
voir. B, a pipe by which a communica- 
tion with the mains of the public water- 
works was established. C, a pipe for de- 
livering the water. 
The height of the vessel was three feet ; 
greatest diameter eighteen inches, least 
diameter twelve inches. 
Some days had elapsed, during which I 
was unable to offer any explanation of the 
phenomenon ; but having mentioned the 
occurrence to another highly respectable - 
and intelligent plumber, Mr. Ewing, he 
alleged that facts no less surprising had 
fallen within the range of his experience. 
He had known an opening made in a leaden pipe at one time, to be 
closed at another, by some unaccountable inward pressure; and, 
upon one occasion, a small fish to be caught in the fissure. 
It then occurred to me that the phenomenon of the collapse had 
been the consequence of circumstances the inverse of those which 
are known to take place in the water ram of Montgolfier, in which 
water, while flowing rapidly in a trunk, being stopped suddenly in 
front, is made to produce a jet rising above the level of the head to 
which the current arrested is indebted for existence. 
The momentum of the water which is in that case expended in a 
jet, must, in the case in which an arrestation takes place in the rear 
of a given portion of the stream, continue to propel that portion di- 
rectly forwards, causing an hiatus or vacuum between it and the 
valve or cock by which the stoppage has been effected. 
The inward pressure, or suction, arising from such a momentum, 
was demonstrated by Venturi ;* and has latterly been ingeniously 
* Nicholson’s Journal, 4to series, Vol. ii. p. 172. 
