PRESIDENTIAL ADDRESS, B.A. 1871. 177 



perature, and have obtained results which seem to 

 show that a highly attenuated gas, which at a high 

 temperature gives several bright lines, gives a 

 smaller and smaller number of lines, of sufficient 

 brightness to be visible, when the temperature is 

 lowered, the density being kept unchanged. I 

 cannot refrain here from remarking how admirably 

 this beautiful investigation harmonises with An- 

 drews' great discovery of continuity between the 

 gaseous and liquid states. Such things make the 

 life-blood of science. In contemplating them we 

 feel as if led out from narrow waters of scholastic 

 dogma to a refreshing excursion on the broad and 

 deep ocean of truth, where we learn from the 

 wonders we see that there are endlessly more and 

 more glorious wonders still unseen. 



Stokes' dynamical theory supplies the key to the 

 philosophy of Frankland and Lockyer's discovery. 

 Any atom of gas when struck and left to itself 

 vibrates with perfect purity its fundamental note or 

 notes. In a highly attenuated gas each atom is 

 very rarely in collision with other atoms, and there- 

 fore is nearly at all times in a state of true 



VOL. II N 



