356 f Assembly 



enter, these pins are bent at right angles, and pass upwards into the 

 outer frame ; freedom of play is thus given them to assume the per- 

 pendicular. In this model, as in most float boards, the figure is that 

 of the parallelogram, this is not the most effective form. Mr. Rennie 

 has shown that the trapezoid figure is equally effective, and is the 

 basis of a patent which he has taken out in England for propelling 

 wheels. 



There is a good application of the wheel and axle in the hoisting 

 platform, which may be seen on the bridge, and of which we have a 

 small model on the table. With that power, and the aid of a few 

 fixed pulleys, those tables may be made to rise successively out of 

 each other, and rising to a great height, serve to convey building ma- 

 terials to the upper platform of a building, saving the continual ascent 

 and descent of laborers on a ladder. There appears to be no other 

 limit to its power than the stability of the wooden frame work, and 

 the strength of the cord which plays over the pulleys. There are two 

 sets o,r platform tables which alternately rise and fall, but which may 

 be made to work singly by putting one cord out of gear. The pinion 

 of the axle is turned by a wheel : by the addition of another wheel 

 intervening, power would be exerted more advantageously, and with 

 rope an inch thick playing over the pulley, a weight of one thousand 

 pounds might be raised up. The saving to builders, by the use of 

 this machine, would be great, for human power is never exerted to 

 worse effect, than in carrying a weight up a height. Thus, if a man 

 going in a horizontal line be able to carry fifty pounds per eight hours 

 (one day) at three miles per hour, the same man can only carry six- 

 teen pounds per four hours at the rate of one and a half miles an hour, 

 the difference being as twelve and a half to one in favor of the hori- 

 zontal line. Tlus is no small saving which may be accomplished by 

 this machine ; it has also been suggested as a good fire escape- 



The patent windlass exhibited, is a beautiful piece of mechanism; 

 the windlas,s is turned by a capstan, and these can be brought to bear 

 upon the anchor and the sails at the same time: the hollow axle and 

 the varied movements of the windlass itself must recommend it as a 

 machine which will economize the hands on ship-board very much, 



