8 IMr. Hill on the Oynithorhymhin parc/do.riis. 



deptlis, or whetlier one of them may be combined wiUi a weight 

 to be used for muintaining the horizontality of the platform. 



7. If by the same means the whole machine Dioves more 

 slowly than the current, we shall have some purchase to -jomk 

 upon, so as to modity its direction in the current. Something 

 like tacking at sea was suggested by Mr. Edgewoith, who 

 proposed that a plane should be attached to the balloon, and 

 placed at an angle to the horizon, so as to modify the direc- 

 tion in rising and falling. If such a plan be practicable, the 

 platform suggested above, may be raised or lowered at anj- 

 angle, so as to answer the purpose. Others have been led by 

 analogy to propose sails and rudders, obviously useless, while 

 the machine was in an equilibrium of indiffei'ence as to posi- 

 tion, moving as fast and together with the fluid in which it 

 floated. If the preceding suggestions are all well founded, 

 something like a moveable keel, either above or below the 

 platform, would answer the purpose of sail and rudder ; or a 

 fixed keel, a rudder and sails may all be tried. I'oo much 

 has been expected ; it will be a great triumph in mechanics, 

 even to gain a few points on the ciu'rent of wind ; navigation 

 at sea offered little more for ages. 



8. It is lookhig too much forward to estimate the time when 

 the balloon shall attain the perfect and independent movements 

 of the steam-boat ; we may however sai'ely say with Darwin, 

 that the steam-engine will also triumph here. We may say 

 that it will not succeed by any imitation of the wings of birds, 

 which are not solely for progressive motion, but are also used 

 for maintaining them in the air. The latter object is moi-e 

 conveniently attained by a balloon, which may be compared 

 to the air-bladder enabling the fish to rise and sink in the 

 water. Analogy refers us to the motion of the salmon against 

 the most rapid stream, which is efliicted by vibrations of the 

 tail, actuig like the oar at the stern of a canoe. 



IV. On the Ornithorhynchus paradoxus or MuUingong, its 

 venomous Spur, and general Structure. By Mr. Patrick 

 Hill, Surgeon in the Royal Naiy*. 



" "Y^OU will be gratiled to learn, that I have been completely 

 -*- successful in establishing our friend Sir John Jamison's 

 account of the spur of the Ornithorhynchus paradoxus. I sub- 

 join an extract from my notes: ' Sunday, Oct. 1, 1820. — On 

 the banks of Campbell's River. In the morning shot a male 



* From a Letter to the Secretary of the Linncan Society; dated 

 Sydney, New Soutli Wales, Nov. .'?, 1831. Tninsactioiis, vol. xiii.' Part II. 



Orni- 



