222 Effect of Temperature on the Viscosity of Gases. 



upward, much more so than S Y. Obermayer's further series 

 with capillary " D " is of much value. It is represented in 

 the line g h, and the three marked points indicate the points 

 yielded by the experiments. This line is also decidedly 

 convex upward, and its curvature seems to be beyond the 

 range of variable errors of measurement. I have connected 

 the individual points with each other by a broken line, because, 

 owing to the small number of points, almost any form of 

 curve could be drawn through them, and to select any one 

 equation would be wholly arbitrary. This remark applies 

 also to the line U V, representing Wiedemann's results. 

 This line is still more convex upward than either of the 

 preceding. The line W X, representing Warburg's results 

 with oscillating plates, is in substantial accord with the 

 results by Obermayer, Wiedemann, and myself, as well as 

 with the mean of Meyer's results ; but as it is derived from 

 observations including but one temperature interval, it cannot 

 serve to determine any beyond the first power variation in 

 the coefficient. 



To show the relation of the several lines to one from an 

 equation of the exponential form which has been so generally 

 adopted, I have drawn the line Z from the equation 



^=(l + 0-003670) ' 76 . 

 Vo 



The fifth series of my own results is shown in the line S Y, 

 the experimental means being denoted by crosses. The 

 deviation of S Y from a straight line is very slight, and I am 

 confident that this is a close approximation to the true 

 result, and that the greater curvature of the lines from my 

 own earlier results and those of other observers is due in 

 part to impurities in the air, either in the form of carbonic 

 acid or of vapour of water. I regard those of my measure- 

 ments on air which precede the fifth series merely as checks 

 upon the accuracy of the process, and as possessing small 

 weight as compared with that series, for reasons assigned in 

 the Critique of the Method. The same is true of all but the 

 last series with carbonic acid. 



Rogers Laboratory of Physics, 



Mass. Institute of Technology, 



Boston, Mass., May 1885. 



