426 THE POPULAR SCIENCE MONTHLY. 



Riglitly interpreted and followed out, these aerial echoes lead to a 

 solution wliich penetrates and reconciles tlie phenomena from begin- 

 ning to end. On this point I would stake the issue of tlie whole in- 

 quiry, and to this point I would, with special earnestness, direct the 

 attention of the Lighthouse Board of Washington. Let them prolong 

 their observations into calm weather : if their atmosphere resemble 

 ours which I cannot doubt then I affirm that they will infallibly 

 find the echoes strong on days wlien all thought of reflexion " from 

 the crests and slopes of tlie waves " must be discarded. The echoes 

 afibrd the easiest access to the core of this question, and it is for this 

 reason that I dwell upon them thus emphatically. It requires no re- 

 fined skill or profound knowledge to master the conditions of their 

 production ; and, these once mastered, the Liglithouse Board of Wash- 

 ington will find themselves in the real current of the phenomena, out- 

 side of which I say it with respect they are now vainly speculating. 

 The acoustic deportment of the atmosphere in haze, fog, sleet, snow, 

 rain, and hail, will be no longer a mystery : even those " abnormal 

 phenomena" w^hich are now referred to an imaginary cause, or re- 

 served for future investigation, Avill be found to fall naturally into 

 place, as illustrations of a principle as simple as it is universal. 



While this Preface was passing through the press, the intelligence 

 of the loss of the Schiller thrilled through the land. 1 look forward 

 to a time when such a calamity upon our coast will be a simple im- 

 possibility. It is in our power to make it so ; and that power will, I 

 doubt not, be promptly and wisely employed. 



Royal Insiitutiox, May, 1875. 



TELEGRAPHIC DETERMI]S"ATIOX OF LOXGITUDE. 



By F. M. GKEEN, 

 iieutenant-commandee united states navy. 



IN^ the construction of new charts for the use of navigators, as well 

 as in the correction of old ones, the assignment of difierent lati- 

 tudes and longitudes to the same point, by various authorities, has 

 always been a source of difficulty and embarrassment. 



The exact position of all prominent points on the coasts of the 

 United States, as well as those of England, France, and other European 

 nations, has been determined with great accuracy; but a large portion 

 of the earth's surface is still very imperfectly and inaccurately laid 

 down on marine charts. 



The latitude of any point being determined directly by observa- 

 tion, and independently of the latitude of any other place, is less likely 

 to be in error than the longitude, which can only be ascertained with 



