62 MR. GEORGE C. SIMPSON ON THE 



protected from extraneous electrical fields and so connected to an electroscope that 

 the rate at which it lost its charge could be measured. By making certain assumptions 

 it can be shown that the charge lost in a small interval of time from any charged 

 body exposed to the air is always a definite fraction of the charge on the body. 

 Thus, when ELSTER and GEITEL had found the charge lost by their cylinder in a 

 minute, they were able to express the loss as a percentage of the charge on the 

 cylinder, and then, by applying this percentage to the charge on the earth, were able 

 to find the quantity of electricity being dissipated from every square metre of surface 

 each minute. 



Besides knowing the amount of electricity dissipated from the surface which 

 depends upon many factors it became also of great importance to know to what 

 extent the air is ionized at any moment. For this purpose EBEKT* designed an 

 instrument which gives the amount of ionization independently of everything else. 

 A known quantity of air is drawn through a cylinder condenser, the inner cylinder ol 

 which is connected to an electroscope. As the air passes between the cylinders 

 the charged inner one attracts t< it all the ions of the opposite sign. These ions 

 neutralize an equal amount of electricity, and so the charge lost by the inner cylinder 

 is a measure of the number of ions contained in the known quantity of air which has 

 been drawn through the instrument. In this way it is possible to find how many 

 electrostatic units of each kind of electricity are free in a cubic metre of air. 



These two instruments are very powerful weapons for attacking the new problems 

 of atmospheric electricity, and have been used as such to a large extent on the 

 Continent. Systematic observations of the dissipation were undertaken by ELSTER 

 and GEITEL, and quite a number of other physicists have devoted themselves to 

 finding the relations existing between meteorological conditions, ionization, the rate 

 of dissipation and the potential gradient. As a result of this work the electrical 

 conditions of the atmosphere are already fairly well known for lands lying within the 

 temperate zone. With the idea of extending this knowledge to places within the 

 Arctic Circle I was granted permission by the Commissioners of the 1851 Exhibition 

 Scholarship to undertake a year's work on atmospheric electricity in Lapland. 

 The work which I proposed to do was the following : 



1. By means of a Benndorf self-registering electrometer to obtain daily curves 



of the potential gradient and from these to calculate the yearly and 

 daily variation. 



2. To make systematic observations of the dissipation by means of ELSTER 



and GEITEL'S instrument. 



3. To make corresponding measurements of the ionization with EBERT'S 



apparatus. 



* Short description, ' Phys. Zeit.,' 2, p. 662, 1901; fuller description, ' Aeronautische Mittheilungen ' 

 p. 1, 1902. 



