OF AIR AND OTHER GASES. 21 



the fifth and sixth readings, with the sum of ten successive amplitudes deduced 

 therefrom. 



Table II. shews the results of this operation as extended to the rest of 

 experiment 62, and gives the logarithmic decrement for each successive period 

 of ten semivibrations, with the mean time and corresponding mean logarithmic 

 decrement. 



Table III. shews the method of combining forty experiments of different 

 kinds. The observed decrement depends on two unknown quantities, the viscosity 

 of air and that of the wire. 



The experiments are grouped together according to the coefficients of p. 

 and K that enter into them, and when the final results have been obtained, 

 the decrements are calculated and compared with the results of observation. 

 The calculated sums of the decrements are given in the last column. 



Table IV. shews the results of the twelve experiments with the fifth arrange- 

 ment. They are arranged in groups according to the pressure of the air, and 

 it will be seen that the observed values of L are as independent of the pressure 

 as the calculated values, in which the pressure is taken into account only in 

 calculating the value of x in the fifth column. By arranging the values of 

 L L' in order .of temperature, it was found that within the range of atmo- 

 spheric temperature during the course of the experiments the relation between 

 the viscosity of air and its temperature does not perceptibly differ from that 

 assumed in the calculation. Finally, the experiments were arranged in order of 

 time, to determine whether the viscosity of the wire increased during the experi- 

 ments, as it did when steam was first used to heat the apparatus. There did 

 not appear any decided indication of any alteration in the wire. 



Table V. gives the resultant value of /A in terms of the different units 

 which are employed in scientific measurements. 



Note, added February 6, 1866. In the calculation of the results of the 

 experiments, I made use of an erroneous value of the moment of inertia of the 

 disks and axis =1 '01 2 of the true value, as determined by six series of experi- 

 ments with four suspension wires and two kinds of auxiliary weights. The 



