294 ME. CLERK MAXWELL ON THE VISCOSITY 



determine the values of jOi, and K. Seven of these had the first arrangement, six had 

 the second, six the third, nine the fourth, and tvi'elve the fifth. 



The values of Q for the five cases are roughly in the proportions of 1, 2, 4, 6, 12, so 

 that it is easy to eliminate K and find |u,g. I had reason, however, to believe that the 

 value of K was altered at a certain stage of the experiments when steam was first used 

 to heat the air in the receiver. I therefore introduced two values of K, K, and Kj, into the 

 experiments before and after this change respectively. The values of K, and Kg deduced 

 from these experiments were 



In ten single vibrations. 



K.=-01568 

 K,= -01901 



The value of [ji^ in inch-grain-second measure at temperature f Fahrenheit is for air 



^=•00001492(461°+^). 



The value of L was then calculated for each experiment and compared with the ob- 

 served value. In this way the error of mean square of a single experiment was found. 

 The probable en-or of [jij, as determined from the equations, was calculated from this and 

 found to be 0*36 per cent, of its value. 



In order to estimate the value of the evidence in favour of there being a finite amount 

 of slipping between the disks and the air in contact with them, the value of L for each 

 of the forty experiments was found on the supposition that 



/3=-0027 inch and ,!i=(-000015419)(46r+O. 



The error of mean square for each observation was found to be slightly greater than 

 in the former case ; the probable error of /3 was 40 per cent., and that of |U/=1'6 per cent. 



I have no doubt that the true value of /3 is zero, that is, there is no slipping, and that 

 the original value of (jo is the best. 



As the actual observations were very numerous, and the reduction of them would 

 occupy a considerable space in this paper, I have given a specimen of the actual working 

 of one experiment. 



Table I. shows the readings of the scale as taken down at the time of observation, with 

 the times of transit of the middle point of the scale after the fifth and sixth readings, 

 with the sum of ten successive amplitudes deduced therefrom. 



Table II. shows 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, veith 

 the mean time and corresponding mean logarithmic decrement. 



Table III. shows 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 /x and K that enter 

 into them, and when the final results have been obtained, the decrements are calculated 



