82 INTRODUCTION. 



faintly shining water, because, if the light is in the 

 water itself, it must shine afterwards ; but if it 

 comes from animalculge, these will shine in the 

 strainer, if slightly shaken. Whether the light 

 which is observed on dead fish before the com- 

 mencement of putrefaction, likewise comes from 

 living animals (as is highly probable) is for the 

 natural philosopher to examine in his study with 

 the microscope. It is rather the business of the 

 physiological naturalist, and the chemist, than of 

 the mariner, to analyze the nature of the (often 

 strongly luminous) molluscae, the medusae, &c. 

 concerning which Mitchell has published such in- 

 teresting observations, in the Medical Repository 

 ofNew York, Vol. IV. 



We have yet to mention the luminous pheno- 

 mena that are observed in the air ; these are, the 

 Aurora Borealis, the fire-balls, and the falling 

 stars. In the first, the observer has to determine 

 the height of the arc bounding it, either by the 

 sextant, or, when the darkness of the horizon 

 does not admit of this, by means of the stars which 

 shine through it, also noting the true time. The 

 extent of it on the horizon, the quickness with 

 which it rises above the horizon to different 

 heights, are likewise objects for his observation. A 

 circumstantial description of them, and even a 

 drawing, which looks very well, when done on dark 

 blue paper, with black and white chalk, are contri- 

 butions to the history of meteors, not to be despised. 



