[MCLENNAN] EARTHS PENETRATING RADIATION 5 
possibility of air containing active emanations entering it during the 
course of the observations. A small aneroid barometer was supported 
inside the receiver with its face directly in front of a glass window 
sealed into the wall of the vessel, and tests made with it from time to 
time showed that the sealing remained secure and intact throughout all 
the measurements. 
In making these tests the receiver was carried from a cool room 
either to a warm one or out into the bright sunshine. This procedure 


MU 
was always followed by a rise in the barometric reading owing to the 
air in the vessel becoming heated. While the receiver was kept in the 
warmer position the high reading was always steadily maintained; but 
on taking it back to the cooler place, the reading just as regularly 
rapidly fell to its former value. This behaviour showed that no air 
escaped from the receiver during the period when the pressure was 
greater than that of the atmosphere outside. 
