932 



SCIENCE 



[N. S. Vol. XXX. No. 782 



sliould be placed in front of a dead black 

 screen and illuminated by a shielded lamp. 

 A reading glass will aid considerably in ob- 

 serving the formation of the drops. 



First determine the critical ratio, i. e., the 

 expansion at which drops just begin to form 

 in dust-free air. Now produce expansions of 

 gradually increasing amoimts and note the 

 cloud eifects. A typical series is given in 

 Table I. 



As Thomson pointed out, after once drops 

 have been formed in dust-free air they will 

 form for some time after for expansions less 

 than the critical value. Hence before another 

 series is taken the bulb B.B should be worked 

 for moderate expansions to free the bulb B of 

 nuclei. In Table II. are recorded two observa- 

 tions taken from each of ten different series 

 similar to that given in Table I. The first ob- 

 servation, the critical expansion, is when 

 drops first appeared, and the second is the 

 next succeeding observation. This is recorded 

 in the table to show how rapidly, yet uni- 

 formly, the drops increase by a slight increase 

 in the expansion. 



TABLE II 



Critical Expansion in Dust-free Air 



Average of those marked (*) 1.31. 



The average value of the critical ratio is 

 1.31. It should be noticed that the greatest 

 variation from this mean is only 1.5 per cent. 

 — a rather close agreement when we consider 

 that the observations were made with two dif- 

 ferent tubes, and also that they extended over 

 three or four weeks. 



It was shown by Wilson that an ionizing 

 agent is an important factor in the formation 

 of drops in dust-free air. Various agencies, 

 such as light from an incandescent lamp fila- 

 ment, the radiation from radium, the Roent- 

 gen rays, etc., were tried, each showing a de- 

 cided effect. On placing a small glass capsule 

 containing 10 milligrams of radium bromide 

 of 200,000 activity within the bulb B a mean 

 value of 1.27 was obtained for the expansion 

 necessary to form drops. Care was taken to 

 free the expansion chamber of dust particles, 

 also to correct for the change in volume caused 

 by the introduction of the small glass tube 

 containing the radium. Again, with this 

 simple apparatus it is not difficult to compare 

 quantitatively the electrification when air is 

 agitated with pure water, with a saturated 

 common salt solution, and with mercury. 

 The effects were all quite marked and the 

 values obtained for the expansions could be 

 repeated consistently at will. 



Chas. T. Knipp 

 University of Illinois 



system of basketry technic 

 Only in recent years have anthropologists 

 interested themselves so generally in the in- 

 dustrial arts of primitive peoples. With this 

 awakening interest has come the appreciation 

 of the prominent place occupied by the cruder 

 forms of weaving — namely, basketry — in the 

 domestic economy of these simple households. 

 It has assisted in the sheltering, the clothing 

 and the feeding of tribes in many parts of the 

 world. This wide distribution of locality, as 

 well as that of usefulness, enables one to bet- 

 ter understand the multiplicity of technics 

 which are constructed of materials from so 

 many climes, and in a manner to fit such a 

 diversity of use. With the aggregation of 



