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 mew of giving the 

 members of the Royal Institution some notion of a man regarding whom 

 many of them linen but little. I tried at the same time to draw up a 

 brief account of Young's labours on the Hieroglyphics 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 par- 

 ticular field, the record of his achievements will be rendered more 

 Complete by it* introduction JiereJ\ 



