506 proceedings: Washington academy of sciences 



has never been found to exceed 2.4' for a height of eye of 18 to 24 

 feet. 



A short description of the Pulfrich dip -measurer was given with an 

 account of the difficulties of observing at sea both with this instrument 

 and all instruments in general. 



The paper concluded with an exhibition of the results of an adjust- 

 ment of all the observations made on the Galilee and those made on the 

 recent cruise of the Carnegie. 



Comparisons with the results of other observers were shown as well 

 as comparisons with the standard tables. 



The latter comparisons showed that the standard tables of dip-bf- 

 horizon are sufficiently accurate for the navigator and cannot be im- 

 proved by the introduction of a temperature or a temperature-differ- 

 ence argument when the result is required for the oceans. 



The 807th meeting was held at the Cosmos Club, May 11, 1918. 

 President Burgess in the chair; 42 persons present. The minutes of 

 the 806th meeting were read in abstract and approved. 



The first paper on The constitution of the gas ion was presented by 

 A. Q. Tool. This paper was illustrated by lantern slides. 



The mobility of the negative ions was determined by three closely 

 related methods. The first was the usual alternating potential method, 

 which is a modification of Rutherford's original method. This gave 

 values which were larger than that for the so-called normal ions, where 

 the normal ion is defined as the ion whose mobility obeys the law 

 u = kP. These large values were shown to be due to numerous fast 

 ions still growing as well as a large number of electrons. 



The second method may be considered as the reverse of the one 

 above, the potential in the positive or accelerating half period being 

 maintained constant while that in the negative half period was varied 

 in determining the current curve. A "critical potential" was then 

 found from the break in this curve which gave mobihty values as low 

 or lower than that usually obtained for the normal ion. This indicated 

 the presence of ions larger than the normal ion. Their mobility 

 obeyed the law cited above. 



The third method made use of the relation existing between the 

 usual saturation current curve and the current curve obtained in 

 Rutherford's method when the alternating potential is produced by a 

 rotary commutator. By this third method it was possible to show 

 something of the mobility distribution of the ions in a gas. Large 

 numbers of normal ions were found to exist at all pressures in air even 

 when carefully dried. 



Through the use of these three methods it was possible to detect ion 

 growth, also ion disintegration. This latter was especially marked in 

 air nearly saturated with water vapor. The results strongly supported 

 the complex ion theory. 



The second paper, on Corresponding changes in the earth'' s magnetic 

 state and in solar activity, 1888-1916, was presented by Mr. L. A. Bauer 

 and was illustrated by lantern slides. 



