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. XYII. — On Compound Engines. By William Lodder. 



[Read before the Auchland Institute, 19^/i 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 Newcastle-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 efifected, 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, 

 and with equally good results. 



The engines were compounded simply by the addition of high pressure 

 cylinders, of 9 inches diameter, fixed above the existing cylinders, the piston 



