398 W. A. Norton on Ericsson’s Caloric Engine. 
escape through the regenerator, must undergo a continual dimi- 
nution of temperature, as it parts with its heat to the successive 
disks of wire-netting, and on the other hand the entering cold 
air, on passing through the successive disks, which are of a higher 
and higher temperature, will tend to lower the temperature of 
each one of these disks, and at the same time to increase the 
difference of temperature between the outer and inner surfaces of 
the regenerator, and thus to compensate for the tendency to equi- 
librium of temperature produced by the flow of heat from the 
inner towards the cooler outer surface. For, while it will reduce 
the temperature of the outer surface, if the regenerator has suffi- 
cient thickness, nearly to an equality with the temperature of 
the external air, the inner surface being exposed towards a highly 
heated enclosure will be less affected. It is to be observed that 
the temperature of the external surface of the regenerator cannot 
at any time be greater than that of the air escaping through the 
pipe 7, and that the temperature of the internal surface can never 
be less than that of the air issuing from this surface, on its pas 
sage into the working cylinder, or rather, heating chamber. 
The preparation necessary for starting the engine consists 
“keeping up a slow fire in the furnaces, for about two hours, 
until the various parts contained within the brick work sball 
have become moderately heated, and then charging the receiver 
with air by means of a hand-pump,” until the guage shows @ 
pressure of about eight pounds above that of the external ait. 
The upper valve, g, is then opened by a starting bar, an 
compressed air flows into the working cylinder, and begis the 
work of raising the piston. 
We are now prepared to inquire into the 
THEORY OF THE MOTIVE POWER OF THE ENGINE. 
[will first state a few principles which it is important should 
be kept in view. 
1. The expansive force of the heated air under the working 
piston must be somewhat less than that of the compressed alr 10 
the receiver; otherwise the air in’ the receiver would have ne 
tendency to flow from it into the heating chamber. The differ- 
ence may not amount to more than a few ounces; it depet 
on the obstructions that exist to the free flow of the air and 
the relative size of the aperture of- communication and heating 
oe When the air is flowing from .the supply cylinder into ct 
receiver its elastic force must exceed that of the air 1” ~ 
ceiver; for the additional reason, beside that just stated, that t of 
valves in the supply-piston would close if no such difference 
pressure. Wie eels : = 
. 
