136 Mr. J. Parnell on a new Fluorescent Substance. 



give velocities of 52 and 29 feet per second respectively. There- 

 fore 



0-88 x 23 



52 x 29 x 32 x 0000002 x 0-25* 



if = 843 seconds or 14 minutes; 



so that the Cape-pigeon could sail half as long as the Albatros, 

 the resistance of the air being supposed to be proportionately 

 the same in both cases. This is more than we should expect, 

 considering the great difference of weight of the birds, but is 

 owing to the small terminal velocity of the Cape-pigeon. It 

 must, however, be observed that although it seems that under 

 favourable circumstances a Cape-pigeon could sail for 14 mi- 

 nutes, the velocity of 29 feet a second is so small that, in order 

 to make headway against the wind, it would have to stop sailing 

 and use its wings long before it had reached its least possible 

 velocity ; so that it could not sail for long without being carried 

 away by the wind, neither could it sail at all in a strong gale, 

 except when sheltered by the waves ; and this answers very well 

 to what we observe ; for in a gentle air the Cape-pigeon sails 

 longer than the Albatros, but hardly ever in a gale. Once du- 

 ring a fresh gale, the air moving probably 70 or 80 feet a second, 

 when standing at the stern of the ship, a Cape-pigeon was blown 

 into my hands and I caught it. 



In the foregoing brief remarks I do not pretend to have done 

 more than indicate the principles involved in the flight of the 

 Albatros when sailing along without moving its wings. The 

 problem still remains to be solved ; but until some experiments 

 have been made on the resistance offered to the air by the front 

 and lower surfaces of birds, a tolerably accurate solution is not 

 possible ; and I hope that some person with the necessary oppor- 

 tunities and means may be induced to take up this highly inter- 

 esting subject. 



XV. Note on a new Fluorescent Substance. 

 By John Parnell, M.A. y F.R.A.S* 



WHEN aniline is heated with mercuric chloride, besides the 

 ordinary formation of aniline-red, a substance is pro- 

 duced in no inconsiderable quantities which possesses such a re- 

 markable fluorescence that the author, not having been able to 

 find any notice of it hitherto published, cannot but think it 

 must up to the present time have escaped observation. The 



* Communicated by the Author. 



