1836.] 



Prop on an inclined Plane. 



126 



But, to show that our critic's reasoning is erroneous, with 

 reference to a prop he asserts that " P is greatest when B C 

 is greatest," and that " P is greatest when B C comes into 

 the vertical position/' for into the direction A C). But now 

 draw all the B Cs as in the annexed figure and carry them 



on to an extent bordering 

 "C on infinity. The last is grent- 



/; v^V. est of course (not A C) ; and 



/ I \ ' ■■ ■.* '-•>■ where is he ? Why with the 



H~f*- -^L^ \ v v""*- N weight at one end of a long 



~^fr • lever almost horizontal, and 



^ ^ ^, the support at the other ; the 

 very weakest position possi- 

 ble. 



The fact is, people who discuss this matter, like the " would- 

 be Mathematician, 5 - 5 do not recollect that the proportion or 

 equation is, in this problem, purposely altered, and that the 

 only point to determine is how the change on one side will 

 affect the other. To preserve an equilibrium, or the propor- 

 tion, our friend argued correctly ; that is, when B C is great- 

 est, P, or the power, must be increased or made greatest, to 

 preserve the equilibrium (the necessity for which we want to 

 avoid), and which is the same as saying when B C is least, P, 

 the power required to restore the balance, is least, (the very 

 thing desired), or, in other terms, when B C is least, the ori- 

 ginal P (without alteration) is greatest. It is worthy of 

 remark that the system now adopted at Chatham for Mine 

 Frames, after long discussion and experiment, accords with 

 this theory. The props, in descending galleries, are always 

 placed perpendicular to the inclined plane. 



Hoping you will excuse this long dissertation, believe me 

 that you have a sincere friend to the Journal, in 



A MINER, 



Note. — Is not the point, discussed in the foregoing papers, one involv- 

 ing a question of practice, as much as of pure science ? — It seems rea- 

 sonable to suppose that a vertical prop, must be a better support to a di- 

 rect downward pressure, than a sloping prop : but it is quite as reason- 

 able, on the other hand, to suppose that a prop at right angles to the 

 shaft of the mine, would be found the most convenient and sufficiently 

 effectual in practice, and that therefore it may be preferred. It is cer- 



