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MISCELLANEOUS INTELLIGENCE. 



§ I. Mechanical Science. 



1. On Measuring the Force of Pressure, by Mr. Bevan. — Mr. 

 Bevan describes his highly useful and applicable method in the 

 following manner : — " If we take a leaden bullet of any determinate 

 diameter, and expose it to pressure between plates of harder metal, 

 made to approach each other in parallel position, the bullet will be 

 compressed or flattened on two opposite sides in an equal degree : 

 provided the lead is pure the degree of compression will indicate 

 the amount of pressure. With a graduated press of the lever kind 

 it will be easy to form a scale of pressure corresponding to the dif- 

 ferent degrees of compression, until the ball is reduced to a flat 

 circular plate of about one-fifth of an inch in thickness ; and it will 

 be found, that an ordinary bullet, of about five-eighths of an inch in 

 diameter, will require a pressure of near 4000 pounds to effect this 

 degree of flattening. Suppose, therefore, we wish to measure an 

 actual pressure supposed to be nearly 20 tons, we have only occa- 

 sion to place 10 or 12 of these balls at a proper distance asunder, 

 so as not to be in contact when expanded, and then to measure, by 

 good callipers, or other suitable means, the compression of each ball 

 either by its thickness or diameter, and afterwards add into one 

 sum the particular pressure due to each ball, from the scale first 

 made, by using the lever press before mentioned." 



By this mode I have ascertained the amount of friction of an 

 iron screw press, with rectangular threads, to be from three-fourths 

 to four-fifths of the power applied ; or the actual pressure has not 

 exceeded 4 or 5 tons ; when the calculated pressure, if there had 

 been no friction, would have been 20 tons. 



The larger the ball the greater will be the pressure necessary to 

 reduce it to a given thickness. An ordinary leaden shot of one- 

 eighth of an inch diameter will require nearly 100 pounds to com- 

 press it into a flat plate. By using a ball five-eighths of an inch 

 diameter, I have found the actual pressure of the common bench 

 vice to be about 2 tons ; when under the same force, if there had 

 been no friction, the pressure would have been 8 tons. 



In the practical application of these balls it will be convenient to 

 make a small impression upon them with a hammer before they are 

 placed between the plates, to prevent them from rolling out of their 

 proper position : this operation will not be found to interfere with the 

 result, as it is the ultimate compression only that is sought, and which 

 is not affected by that of a smaller degree before impressed. Hence 

 the same substance may be used several times, provided the suc- 

 ceeding pressure exceeds that of the preceding. 



It may be observed, that the application of these leaden balls to 



