102 ANNUAL EECORD OF SCIENCE AND INDUSTRY. 



be interchanged between international systems for storm 

 warning. The physical laws, according to which the mo- 

 tions in the atmosphere take place, are at j) resent still too 

 little understood to enable us to determine exactly before- 

 hand the i^ath which any storm that is already known to ex- 

 ist on the earth's surface will subsequently take. The cau- 

 tious observer notes the barometer, and the thermometer 

 also, the direction and strength of the wind, as well as the 

 appearance of the heavens, the kind of clouds, the direction 

 of their motion, and the condition of the sea, and seeks to de- 

 termine from these elements whether a storm exist in any 

 direction in his neighborhood. But all these data still leave 

 it uncertain in which direction the storm will move. The 

 observer knows not whether the storm-path will pass over 

 him or to one side of him. The uncertainty is completely 

 removed if the observer knows also the condition of the at- 

 mosphere with the same accuracy at a number of points in 

 his neighborhood, and in this resj^ect it is that the telegraph- 

 ic weather notices become of service ; and it is bis experi- 

 ence that the dissemination of such knowledge in the sea- 

 ports along the coast of the Netherlands, as it has taken 

 place now since 1860 under the direction of Buys Ballot, 

 has proved highly useful to the marine service. In the most 

 recent times the warnings of the storms have been graphic- 

 ally exhibited by means of the aeroklinoscope, an instrument 

 whose invention is due to Prestel, and which takes the place 

 of semaphores, or such other signals as have sometimes in 

 Holland been exhibited from lio-ht-houses. But the diffi- 

 culty of perceiving an}'- signal from a distance in the thick 

 weather that precedes a storm has prompted Prestel to in- 

 vent still another instrument, which he calls the storm-warn- 

 er, which is sometimes constructed in the form of a diagram 

 that can be laid upon a nautical chart, and, being properly 

 adjusted by the observed wind and barometric gradient, 

 points out at once the direction in which the storm centre 

 lies. M'gebnisseii der BeohacJitungen. 



ON THE DETERMINATION OF THE ALTITUDE OF THE CLOUDS. 



Professor Dr. Prestel has proposed a method for determin- 

 ing the altitude of the clouds, in which the electric telegraph 

 plays an important part, the trigonometrical principles in- 



