observed at the Kentish Knock Lightship. 129 



p. 249), namely, the presence in the atmosphere of moisture 

 not necessarily in the form of rain or haze, bnt actually 

 present, though not visible, on dark starless nights. In order 

 to put my views on this subject to a scientific test, I took 

 with me to the lightship a hygrometer, with the object of 

 ascertaining the actual percentage of humidity in the air 

 on such occasions. I had not many chances of using the 

 instrument, as either rain or haze was usually present, but 

 on two suitable occasions I found the percentage to reach 

 as high a figure as 86 — a more pronounced residt than I had 

 anticipated. 



There was hardly a single occasion during my visit on 



which the rays were brilliant and the birds absent; on the 



• other hand, there was not a single instance of migrants 



visiting the light when the night was bright and starlight or 



the moon was visible. 



The birds which appear at the lantern are, by some autho- 

 rities, considered to be those that have lost their way, and 

 hence make for the light in default of any other directive 

 impulse. After my experiences at the Eddystone and the 

 Kentish Knock, I am convinced that this is not the true 

 explanation. I believe that the migrants are actually decoyed 

 ' from or arrested on their course by the influence of the 

 light itself. At the Eddystone the emigrants which I saw in 

 such numbers had barely left the land behind them, and had 

 not had time to get lost when they appeared at the lantern. 

 Another important fact in support of my contention is that 

 the birds never appear at the light-stations at night except 

 when the rays are remarkable for their luminosity; and in 

 this connection it is important to bear in mind that this 

 brilliancy does not depend upon such a thickening of the 

 atmosphere as would cause inconvenience to the birds during 

 their passage, for I have seen them in great abundance at 

 the lanterns when I could make out neighbouring lights that 

 were ten miles or more distant. Another significant fact is 

 that they do not seek stations having red or green lights. 

 Such lanterns, I am informed by the keepers, are seldom if 

 ever visited under any conditions, for, owing to the subdued 

 SER. viii. — VOL. IV. k 



