92 



interchanged, and the pan Y containing the weight P, and the pan X 

 containing the weight Q, suspended alternately from the right-hand 

 end of the beam the same number of times. 



In weighing by Gauss's method, in which the two weights to 

 be compared as suspended from the right and left-hand ends of 

 the beam respectively, and are then interchanged, it was desirable 

 to be able to transfer the pans and the weights contained in them 

 from one end of the beam to the other, without opening the 

 doors of the balance-case, and thus avoid sudden changes of tem- 

 perature of air in the balance-case, and consequent production of 

 currents of air. In order to effect this, a slender brass tube 38 

 inches long was made to pass freely through two holes in the ends 

 of the balance-case, which is nearly 23 inches long, near the top of 

 the case and half-way between the balance and the front of the case. 

 To the middle of the tube is attached a depending loop of wire. 

 Suppose that by sliding the tube the loop is brought near to the 

 right-hand end of the beam, and the pan with a weight in it trans- 

 ferred from the end of the beam to the wire loop by a brass rod 

 having a hook at the end, which is inserted through a hole in the 

 right-hand end of the balance-case. By sliding the tube in the 

 opposite direction, the loop with the pan and weight suspended from 

 it, is brought near to the left-hand end of the beam, to which it is 

 transferred by a brass rod having a hook at the end, passing through 

 a hole in the left-hand end of the balance-case. A similar tube half- 

 way between the balance and the back of the case, serves to transfer 

 the other pan and weight from one end of the beam to the other. 

 In this manner any number of comparisons may be made without 

 opening the balance-case, except in the middle of the series, for the 

 purpose of changing the pans. 



A sufficient number of preliminary comparisons of Sp, RS, Sb, K, 

 Ex, L, Ed having been made in 1844, the results were reduced, 

 when the material of one weight was platinum and that of the other 

 brass, to what they would have been in air (=65-66, 6 = 29'75), 

 or, of the mean density of the air during the comparisons of Sp arid 

 RS with U in 1829. Using U, Sp, RS, &c. to denote the apparent 

 weights of U, RS, &c. in air (t=65'66, 6=2975), it was found 

 that 



