LUMINOSITY. 387 



plant and looked steadfastly at it, but could not see 

 the flash again, till we chanced in passing and re- 

 passing to look at it obliquely, and we could then 

 repeat the phenomenon at pleasure. It appeared to 

 be an optical illusion, and that the apparent flash of 

 light was merely the spectral representation of the 

 blossoms of a blue-green." On behalf of the elec- 

 trical view it is urged that the occurrences have been 

 observed at times when the air has been dry and 

 charged with electricity. 



A second class of luminous appearances are of the 

 type of an experience also of the daughter of' 

 Linnaeus with the dittany. When the daughter of 

 Linnaeus one evening approached the flowers of 

 Dictaviniis albus with a light, a little flame was kindled 

 without in any way injuring them. The experiment 

 was afterwards frequently repeated, but it never suc- 

 ceeded ; and whilst some scientific men regarded the 

 whole as a faulty observation, or simply a delusion, 

 others endeavoured to explain it on various hypo- 

 theses. One of them especially which tried to 

 account for the phenomenon by assuming that the 

 plant developed hydrogen found much favour. At 

 present, when this hypothesis has become untenable, 

 the inflammability of the plant is mentioned more as 

 a curiosum, and accounted for by the presence of 

 etheric oil in the flowers. Being in the habit of 

 visiting a garden in which strong healthy plants of 

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