284 THOMAS YOUNG. 



advantage of any mechanical power, however it may be 

 employed, are usually proportional to this product, or 

 to the weight of the moving body, multiplied by the 

 height from which it must have fallen in order to 

 acquire the given velocity. Thus, a bullet moving with 

 a double velocity will penetrate to a quadruple depth in 

 clay or tallow; a ball of equal size, but of one-fourth of 

 the weight, moving with a double velocity, will pene- 

 trate to an equal depth; and, with a smaller quantity 

 of motion, will make an equal excavation in a shorter 

 time. This appears at first sight somewhat paradoxical ; 

 but on the other hand we are to consider the resistance 

 of the clay or tallow as a uniformly retarding force, and 

 it will be obvious that the motion, which it can destroy 

 in a short time, must be less than that which requires 

 a longer time for its destruction. Thus also when the 

 resistance opposed by any body to a force tending to 

 break it is to be overcome, the space through which it 

 may be bent before it breaks being given, as well as 

 the force exerted at every point of that space, the power 

 of any body to break it is proportional to the energy of 

 its motion, or to its weight multiplied by the square of 

 its velocity." 



[The foregoing Essay was prepared with the view of giving 

 the members of the Royal Institution some notion of a man re- 

 garding whom many of them Tcnew but little. I tried at the same 

 time to draw up a brief account of Young's labours on the Hiero- 

 glyphics of Egypt. The subject lay far apart from my usual 

 studies, and this fact, coupled with my'anxiety to avoid offence in 

 dealing with the relationship of Young and Champollion, threw 

 upon me an amount of work to which my health at the time was 

 unequal. Though not included in the Address delivered to the 

 members, this account was published in the "Proceedings of the 

 Royal Institution." Despite its inadequacy to give any just notion 

 of the magnitude of Young's labours in this particular field, the 

 record of his achievements will be rendered more complete by its 

 introduction here.'] 



