November 16, 1906.] 



SCIENCE. 



613 



capacity was found to be practically inde- 

 pendent of the electrolyte so long as water 

 solutions are dealt with. Since, cet. par., 

 the capacity decreases proportionally to the 

 thickness of the film, for the sulphuric-acid 

 films to have a capacity as large as the 

 films formed in other solutions seemed to 

 be contradictory to the observation of 

 others who had investigated the question 

 of the thickness of the films ; the sulphuric- 

 acid films always having been found to be 

 much thicker than those in other solutions. 



Further experiments by the writer have 

 confirmed the results as to the greater thick- 

 ness of the sulphuric-acid film, as well as 

 the fact that they do not have any smaller 

 capacity than the others. With water- 

 cooled tubular electrodes sulphuric-acid 

 films more than 0.3 mm. thick were formed ; 

 but their minimum capacity values were 

 slightly larger than those of other films 

 whose maximum thickness could not have 

 been more than 0.001 mm. Sodium sul- 

 phate gives films similar to those in sul- 

 phuric acid as to both thickness and ca- 

 pacity. 



These results necessitate the conclusion 

 that with the sulphates the insulating film 

 is not the whole film; but that we have, 

 superimposed on the insulating film, whose 

 capacity is measurable, a conducting film 

 many times thicker. For solutions other 

 than the sulphates there is no evidence for 

 any such dual-natured film. 



The resistance of these films as measured 

 by the "Wheatstone bridge with small alter- 

 nating current is much smaller than the 

 apparent resistance as calculated from the 

 residual direct current. 



Bridge measurements were taken both 

 while the direct current was still acting and 

 after it was turned off, while the switching 

 on or off of the direct current made no 

 change in the capacity, the resistance of 

 the films was only about one third as large 

 with the current on as with it off. 



Spark Potentials between a Point aiid 



Plane, for Small Distances: Robert F. 



Earhart, Ohio State University. 



Measurements were made on the P.D. 

 required to cause a spark to pass between a 

 needle point and plane surface. The P.D. 's 

 were secured from an A.C. transformer 

 and were measured with a Weston volt- 

 meter. No. 10 Sharp needles were used as 

 the point electrode. A large number of 

 needles were examined with a microscope 

 and points approximating a pattern needle 

 were chosen. 



Distances separating the electrodes were 

 measured with an interferometer. 



Curves representing the relation between 

 spark-potential and distance are similar to 

 those showing the same relation between a 

 spherical electrode and a plane. 



For air, at atmospheric pressure the so- 

 called 'minimum potential' was found to 

 lie between 290 and 310 volts. 



This value does not agree with results 

 secured by other observers from static 

 machines. The value given by Tamm is 

 2,150 volts when the point is negative and 

 3,300 for a positive point. 



Dayton C, Miller, 

 Secretary of Section B. 



THE 80IENTIFIG INVESTIGATION OF THE 



P8YCHICAL FACULTIES OR PROCESSES 



IN THE HIGHER ANIMALS."^ 



For a consistent investigator there is in 

 the higher animals only one thing to be 

 considered— namely, the response of the 

 animal to external impressions. This re- 

 sponse may be extremely complicated in 

 comparison with the reaction of animals of 

 a lower class. Strictly speaking, natural 

 science is under an obligation to determine 



^ The Hiixley lecture on recent advances in sci- 

 ence and their bearing on medicine and surgery. 

 Delivered by Professor Ivan P. Pavlov at Charing 

 Cross Hospital on October 1, 1906. From the 

 report in the British Medical Journal. 



