OS THB VISCOSITY OB INTERNAL FRICTION 



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 /v I had reason, however, to 

 U-lieve that the value of K was altered at a certain stage of the experiments 

 whrn steam was first used to heat the air in the receiver. I therefore intro- 

 iluced two values of A", A', and A',, into the experiments before and after this 

 rliange respectively. The values of A', and A", deduced from these experiments 

 were 



In ten lingle vibrations. 



A", = -01568 

 AT, = -01901. 



The value of ft in inch-grain-second measure at temperature ff> Fahrenheit 



is for air 



/x = -0000 1492 (46 1 + 0). 



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

 the observed value. In this way the error of mean square of a single experi- 

 ment was found. The probable error of /x, 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 



=0027 inch and ^ = ('000015419) (461 



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

 greater than in the former case ; the probable error of ft was 40 per cent., and 

 that of /t = 1 '6 per cent. 



I have no doubt that the true value of ft is zero, that is, there is no 

 slipping, and that the original value of ft 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. shews the readings of the scale as taken down at the tune of 

 observation, with the times of transit of the middle point of the scale after 



