42 Prof. C. Barus on the Absorption of the 



2. The method of experimentation has been indicated in my 

 first paper *, and is based on colour criteria obtainable with the 

 steam-jet. Here I need only recall that a current of mode- 

 rately dry air is furnished by a gasometer-train (Mariotte 

 flask, volume-flask, pressure-gauge, desiccator), terminating 

 in the fine screw-stopcock F. On opening the latter, this 

 passes through the phosphorus-tube P (containing pellets of 

 phosphorus between strips of wire-gauze), where it is highly 

 charged with the ionized emanation. This saturated air is 

 conveyed into the colour-tube C C (old pattern of which j is 

 the simple jet), through the absorption-tube £, of the length, 

 diameter, and material to be examined. The tube t is sealed 

 into P, while the other end dips slightly into the lateral influx- 

 pipe C / of the colour-tube. The arrangement of C (length, &c.) 

 has very little, if any, effect on the results, as was pointed 

 out in my last paper. The draft due to j is sufficient to 

 capture all the nuclei from the open end of the absorption- 

 tube t, and the whole of it is impressed on the jet. 



3. To illustrate the method of work, an example of the data 

 for a single tube is given in the following table (I.). The other 

 results are briefly summarized (Table II.) or expressed in the 

 chart. Length x and radius r refer to the absorption- tubing 

 employed. The volume (V litres per minute) of charged air 

 passing through P is the amount needed to produce a definite 

 colour (full blue) in the field of the colour-tube C. The 

 velocity of the air-current through t is given under v in 

 centimetres per second. The constant k in the final column 

 is the absorption velocity, computed from the equation 



* = 2-65(V/™)log(V/V ), 



where V is the volume in litres per minute giving the iden- 

 tical blue colour when the absorption-tube t is removed, and 

 the phosphorus-tube conveys its contents directly into 0'. 

 The other data (p, the pressure of the steam issuing from the 

 jet, always low, and 6 the temperature of the air at influx 

 measured by the thermometer T) are of little immediate 

 interest. 



In most cases many observations (often four or five) were 

 made for each tube-length x in each series given, the difficulty 

 being to select the same standard blue. The table contains 

 only the mean values. 



* Phil. Mag. [6] vol. i. p. 572 (1901). ; preliminary results in < Science/ 

 vol. xi. p. 201 (1900); Arner. Journal of Science, March, 1901. 



