ave used 778. If the value given by Rowland, about 783
according to the air thermometer at 39 deg. F., should prove to be
correct, it seems probable that the constant 1.406 used above would be
reduced to about 1.403, or that the other constants must be changed by
a small amount. The height of the homogeneous atmosphere used above,
26,214 feet, is the value used by Rankine as deduced from Regnault's
figures, and only one foot less than the value used by Sir William
Thomson; but the figures used by Mr. Hanssen give 26,2101/2 feet.

The method above called Hanssen's is really that of Dr. Mayer (the
German professor), who in 1842 used it for determining the mechanical
equivalent; but on account of erroneous data, the value found by him
was much too small.

* * * * *

ECONOMY TRIALS OF A NON-CONDENSING STEAM ENGINE--SIMPLE, COMPOUND, AND
TRIPLE.[1]

[Footnote 1: Abstract of paper read before the Institution of
Civil Engineers, March 13.]

BY MR. P. W. WILLANS, M.I.C.E.

The author described a series of economy trials, non-condensing, made
with one of his central valve triple expansion engines, with one
crank, having three cylinders in line. By removing one or both of the
upper pistons, the engine could be easily changed into a compound or
into a simple engine at pleasure. Distinct groups of trials were thus
carried out under conditions very favorable to a satisfactory
comparison of results.

No jackets were used, and no addition had, therefore, to be made to
the figures given for feed water consumption on that account. Most of
the trials were conducted by the author, but check trials were made by
Mr. MacFarlane Gray, Prof. Kennedy, Mr. Druitt Halpin, Professor
Unwin, and Mr. Wilson Hartnell. The work theoretically due from a
given quantity of steam at given pressure, exhausting into the
atmosphere, was first considered.

By a formula deduced from the [theta] [phi] diagram of Mr. MacFarlane
Gray, which agreed in results with the less simple formulas of Rankine
and Clausius, the pound weight of steam of various pressures required
theoretically per indicated horse power were ascertained. (See annexed
table.)

A description was then given of the main series of trials, all at four
hundred revolutions per minute, of the appliances used, and of the
means taken to insure accuracy. A few of the results were embodied in
the table. The missing quantity of feed water at cut off, w