144 Transactions. 
the breast to the back, which was before perpendicular, is now inclined to the 
right, part of the upward reaction will be diverted to the right, and will 
therefore turn the bird in that direction. Of course the force thus diverted 
will be taken from that necessary to counteract gravity, so that the bird 
_ would fall if it did not compensate for this loss by increasing the angle to the 
horizon at which it was flying. So that if a bird wishes to turn to the right 
all it has to do is to elevate the left and lower the right side of the body, and 
at the same time elevate the fore and lower the hinder parts of the body ; if it 
wishes to turn to the left, it will elevate the right and fore parts, and lower 
the left and hind parts, and the sharpness of the turn will depend entirely 
upon the angle that the wings,’or rather the line drawn from tip to tip of the 
wings, makes with the horizon. This movement may be easily seen in the 
pigeon, gull, pheasant, or indeed in almost any bird. 
Art. XVII—On Compound Engines. By WILLIAM LODDER. 
[Read before the Auckland Institute, 19th August, 1872.] 
THE engines of the “ Star of the South,” as originally fitted, were inverted, low 
pressure condensers of the ordinary type, with cylinders of 22 inches diameter 
and 18 inch stroke ; nominal horse-power about 27 ; they were manufactured 
by Hawthorne, of Neweastle-on-Tyne, in 1863. 
In June of last year the boiler was found unfit for much further use. It 
then became a matter for consideration what kind of boiler should be adopted, 
and it was finally determined to put in a small multitubular circular boiler, 
capable of sustaining a working pressure of 80 lbs. per square inch at sea ; 
also to compound the engines and introduce a surface condenser. 
It was calculated that by adopting this plan a saving in fuel of one half 
would be effected, the speed of the vessel remaining the same as before. 
Plans and specifications were prepared by Mr. James Stewart, C.E., at 
whose suggestion the compound principle was adopted, and the contract for 
the new machinery and alterations was carried out by Messrs. Fraser and 
Tinne, of Auckland, in a highly creditable manner. 
For the benefit of owners of steamers and others unacquainted with the 
method of conversion of single into compound engines, it may not, perhaps, be 
out of place to explain more fully the plan adopted, because nearly every screw 
steamer running on the coast of New Zealand could be similarly converted, 
= with equally good results. 
_ The engines were compounded simply by the addition of high pressure 
{s of 9 inches diameter, fixed above the existing cylinders, the piston 
