the Atmosphere over the Ocean. 240 



per c.c. to be ra + — 1150, n_ = 800, ratio 1*5. These values 

 do not differ materially from those which obtain in Germany, 

 or Lapland *", or Canada, and they indicate that the ionizations 

 at sea and on laud are approximately the same in magnitude. 



The present paper contains an account of observations of 

 the ionization of the atmosphere made from June 21 to 30, 

 1906, on board the S.s. " Athenia," Donaldson Line, sailing 

 from Montreal to Liverpool. On this voyage the weather 

 was bright and very clear, and there was neither fog nor 

 rain. The barometer was fairly steady, and an ti cyclonic 

 conditions prevailed with northerly winds. The sea was 

 moderate to smooth, the motion of the ship was not great, 

 and at no time was there much spray on deck or in the air. 

 There were few passengers and there was much deck room. 

 The captain and officers were kind and obliging. It will 

 be seen then that the whole conditions were exceptionally 

 favourable. It was possible to select positions for observations, 

 screened from the sun, so that the wind blew fresh from the 

 sea, unmixed with any air from the ventilators of the steamer. 



The instrument used was the later pattern designed by 

 Ebert, made by Gunther and Tegetmeyer, of Brunswick. 

 A small turbine driven by clockwork draws air through a 

 vertical cylinder in which is a charged rod connected to an 

 electroscope. The amount of electricity per cubic metre of air 

 is determined from the fall of potential indicated by the elec- 

 troscope. Assuming that the charge of an ion is 3*4 X 10~ 10 , 

 it is easy to deduce the number of ions present per c.c. The 

 instrument gave complete satisfaction, and there was no 

 trouble about insulation. It may be noted that the key for 

 winding the clockwork wore out on the voyage, but the 

 chief engineer readily found a substitute for it. With care 

 it was possible to obtaiu accurate readings even in a moderate 

 sea, in spite of the motion of the ship. The natural leak of 

 the electroscope has remained small throughout. The only 

 difficulty is that the aluminium leaves are displaced by 

 convection currents when there is a sudden change of 

 temperature. For example, on altering the temperature 

 of a room in Montreal from 61° F. to 20° F. the leaves have 

 opened from 19'7 to 25'8 divisions, indicating an apparent 

 change of voltage from 157 to 178. After a few minutes 

 the leaves returned to their original position, showing that 

 the movement was due to convection currents. It is, therefore, 

 desirable to place the instrument for half an hour or so in the 

 position of observation before beginning to take readings. 



* G. C. Simpson found in Lapland, during 1903-1904,* for the average 

 values, w + =1120, ??_ = 972, ratio 1*2. 



