338 



Profs. Remold and Rucker on the 



[June 21. 



Table I. is an example of the way in which the results required were 

 deduced from the experiments. Column I. gives the cathetometer read- 

 ings in millims. for the positions of the colours whose names are placed 

 opposite. 



The orders of the colours are indicated by the numbers placed after 

 them. The readings for a particular colour were obtained by placing the 

 point of intersection of the cross wires of the telescope in the centre of 

 the band of that colour. In some cases more definite readings could be 

 obtained by taking the line of division between two colours, and such are 

 indicated by writing the names of the two colours one above the other 

 with a line between them. The last colour named is that of the portion 

 of the film extending to the bottom from the point at which the last 

 reading given was taken. 



Column II. gives a similar set of readings taken a little later. 



Column III. the differences between corresponding numbers in I. and 

 II., or the distances through which the colours had moved. 



Columns IV. and V., the number of minutes which elapsed between the 

 first reading given in Column I. and the others given in Columns I. 

 and II. 



Column VI. gives the differences between corresponding numbers in V. 

 and IV., or the number of minutes which elapsed between two observa- 

 tions of the same colour. 



Column VII. gives the quotients of the numbers in III. by the corre- 

 sponding numbers in VI., or the velocity of motion of each colour in 

 millims. per minute. 



.Column VIII. gives the positions of all the colours ten minutes after the 

 first observation (at which time an electrical observation was made), 

 deduced from the previous Columns. 



Column IX. gives the lengths of the sections of the cylinder comprised 

 between the colours named. These are obtained by subtracting the top 

 number in Column VIII. from the reading for the top of the cylinder, 

 viz. 289*7, each of the other numbers from that above it, and by subtrac- 

 ting from the last number the reading for the bottom of the cylinder, or 

 259-3. 



Column X. gives in millionths of a millim. the thicknesses for air cor- 

 responding to the various colours named. 



These data were sufficient to enable the authors to represent graphi- 

 cally the shapes of the films, and they annex (pp. 340, 341) a number of 

 curves drawn for this purpose, of which that numbered VII. is obtained 

 from the set of experiments given in Table I. 



Since the length of the liquid cylinder was 30*4 millims., it is necessary 

 to represent the thickness on a much larger scale than that used for the 

 length. No calculation is needed to allow for the refractive index or for 

 the angle of incidence of the fight, since, by introducing these corrections 

 (which become necessary before the resistance of the film can be calcu- 



