tS4 Mr Sang on the relation which sitbsists 



truths ; they teach us this useful and needful lesson, that there 

 are bounds beyond which no ingenuity can carry us, and toward 

 which we can only hope to approach. How often have men at- 

 tempted to plume themselves with wings ? How many years 

 were spent in search of the golden secret ? How many fortunes 

 have been wasted in the contrivance of perpetual motions ! 

 And, to come nearer the present moment, how many have ruin- 

 ed themselves with the locomotive engine ! This last is the bub- 

 ble of the present day, and on it I shall make a few observations. 

 At the surface of Jupiter a steam-engine of twenty horses' 

 power would be unable to move : at the surface of our Earth, 

 one of perhaps 1000 horses' power might perform pretty well ; 

 but at the surface of the Moon they might be made of perhaps 

 £0,000 horses' power, — supposing the pressures of the atmo- 

 spheres in the three cases to be alike. On Jupiter a steam-car- 

 riage would be an absolute chimera ; on the earth it is barely 

 possible ; but on the moon nothing would be more usual. An 

 intensity of gravitation slightly greater than that which the earth 

 exerts, would altogether preclude the hope of obtaining a loco- 

 motive engine. As it is, on flat rail-roads they perform well ; 

 as the road becomes inclined, they become less practicable ; and, 

 on common roads, nothing but the most consummate skill in the 

 selection and in the use of the material, as well as in the contri- 

 vance of the parts, can ever be successful in their construction. 

 Security demands strength, strength requires weight, weight in- 

 creases the friction, friction calls for additional power, and 

 power can be procured only by an increase of weight. To re- 

 concile these conflicting claims is not the task for a beginner in 

 mechanical contrivance, but for one well versed alike in the 

 theory and in the practice of the arts. Models are of no use, 

 for, although the model be able to climb a considerable ascent, 

 that fact is no guarantee that the full-sized instrument will be 

 able to follow its prototype. Let those who speculate on this 

 matter remember that the elephant inhabits the plains, and 

 leaves the mountains to be tenanted by the smaller tribes ; and 

 let them also recollect, for the fact bears more upon the subject 

 than at first may appear, that the larger animals are most easily 

 exterminated ; that we have the fox and the rat, though the 

 wolf be long since gone. ji. i . 



