lii GENERAL SUMMARY OF SCIENTIFIC AND 



pecially if during the detonation there is a musical sound 

 produced. Fine striae are then observed perpendicular to 

 the axis of the tube. If the tube is very long, there is no 

 musical sound produced, but the rings are widely separated 

 and very sharp. 



La Cour has devised a very ingenious use of the tuning- 

 fork for transmitting signals on telegraph lines, which prom- 

 ises to become of great importance. It is based on the well- 

 known fact that if a given fork be made to interrupt an elec- 

 tric circuit by its vibrations, and the intermittent current 

 thus produced be passed through a series of electro-magnets, 

 each in connection with a fork of different rate, only that 

 fork will be thrown into vibration which is in unison with 

 the first one. Practically the time required to do this is a 

 small fraction of a second. The advantages of this method 

 are numerous. Not only may many receiving instruments 

 at one station be operated, each by its own key, through a 

 single wire, but many different stations in the same circuit 

 may be operated, that one alone receiving the message which 

 has the requisite instrument. Moreover, many signals may 

 in this way be transmitted over the same wire at the same 

 time, and many dispatches sent simultaneously to as many 

 stations. All this may be done, too, without affecting the 

 line for its ordinary use, and independent of atmospheric 

 and terrestrial currents. The system recently patented by 

 Elisha Gray, of Chicago, is essentially similar in principle. 



Mayer has published a redetermination of the durations of 

 the residual sonorous sensations, in which he was assisted by 

 Madame Emma Seiler and her son, Dr. Carl Seiler, of Phila- 

 delphia, well known in connection with similar researches of 

 Ilelmholtz. It now appears that JJt l has a persistence of -^ 

 of a second, Ut 2 ^, Ut 3 T \>, Sol 3 t-J^, Ut 4 y^, Mi 4 j^-, Sol 4 

 -pjr, and Ut 5 T ~jy of a second. The determination is not an 

 easy one, owing to the production of secondary and result- 

 ant tones. 



Pole has made an experimental determination of the 

 change in the pitch of a note which takes place when the 

 sounding body is moving a repetition of the experiment. of 

 Buys Ballot. He used for the purpose locomotive whistles, 

 and concludes that the most common interval by which the 

 tone is lowered when two trains pass each other is a third, 



