LECTURES TO SCIENCE TEACHERS. 



And "by deducting from the sum the logarithm 



(5.) Of the ratio of the density of the standard at C. to 

 the maximum density of water. 



The logarithms of terms 1, 2, and 4 are readily obtained 

 from the printed tables used by the Standards Department, 

 which are those used by Professor Miller, and described by 

 him in his account of the construction of the imperial 

 standard pound in Phil Trans. 1856, Part III. p. 784. 



Of course, in comparing two standard weights of equal 

 density, or where no special scientific accuracy is required, 

 their apparent relative weight in air may be taken as their 

 true relative weight. This, however, will not give their 

 true or absolute weight, which is their weight in a vacuum, 

 unless the exact weight of air displaced by them is ascer- 

 tained. 



37. The time allotted to this lecture does not allow me to 

 explain more fully the mode of computing the weight of air 

 displaced by a standard weight. But a sufficient idea of the 

 effect of the difference of density in standard weights com- 

 posed of different materials may be given from the following 

 table of the weight of air displaced by 1 Ib. avoirdupois 

 weights differing in density. It may be seen that the weight 

 of air displaced is in an inverse ratio to the density : 



Table of the Weight of Standard Air (t = 62 F., b = 30 

 inches) displaced by 1 Ib. avoirdupois weights differing in 

 density : 



38. You may now see a practical illustration of the effect 

 of the difference of density in weights. Here are three 1 Ib. 



