160 FRAGMENTS OF SCIENCE 



rush of the creatures through the water had started the 

 phosphorescence, every spark of which was converted by 

 the motion of the retina into a line of light. Each por- 

 poise was thus wrapped in a luminous sheath. The phos- 

 phorescence did not cease at the creature's tail, but was 

 carried many porpoise-lengths behind it. 



To our right we had the African hills, illuminated by 

 the moon. Gibraltar Eock at length became visible, but 

 the town remained long hidden by a belt of haze, through 

 which at length the brighter lamps struggled. It was like 

 the gradual resolution of a nebula into stars. As the in- 

 tervening depth became gradually less, the mist vanished 

 more and more, and finally all the lamps shone through 

 it., They formed a bright foil to the sombre mass of rock 

 above them. The sea was so calm and the scene so lovely 

 that Mr. Huggins and myself stayed on deck till near 

 midnight, when the ship was moored. During our walk- 

 ing to and fro a striking enlargement of the disk of Jupi- 

 ter was observed, whenever the heated air of the funnel 

 came between us and the planet. On passing away from 

 the heated air, the flat dim disk would immediately shrink 

 to a luminous point. The effect was one of visual per- 

 sistence. The retinal image of the planet was set quiver- 

 ing in all azimuths by the streams of heated air, describing 

 in quick succession minute lines of light, which summed 

 themselves to a disk of sensible area. 



At six o'clock next morning, the gun at the Signal 

 Station on the summit of the rock boomed. At eight 

 the band on board the "Trafalgar" training-ship, which 

 was in the harbor, struck up the national anthem; and im- 

 mediately afterward a crowd of mite-like cadets swarmed 

 up the rigging. After the removal of the apparatus be- 



