C. GENERAL PHYSICS. 81 



is a very small increase, but in some cases even a decrease, of 

 the distance at which the sound is audible. 3. It is probable 

 that with equal volumes of sound in moving water the audi- 

 tory distance will increase with the sharpness of the sound. 

 It is suggested that powerful steam- whistles might be used 

 with great effect, but no attempt has been made to test this 

 question. 6 D, October 19, 1872, 241. 



ELECTRICAL PYROMETER. 



According to the American Chemist, an instrument has 

 been invented which will measure with perfect accuracy the 

 heat of the hottest furnace. It is based on the principle that 

 the resistance of pure metals to the electric current increases 

 with the temperature in a very simple ratio. A platinum 

 wire, of known resistance, is coiled around a cylinder of fine 

 clay, and covered with a tube of the same material. The test 

 is a Daniell's battery, of two cells, and with a resistance meas- 

 urer, and the instrument is placed in the furnace, the tempera- 

 ture of which is to be ascertained. It is then only necessary 

 to read off the indications of temperature on the graduated 

 resistance measure. Amer. Chemist, June, 1872, 476. 



MAGNETIC ACTION OF PETROLEUM. 



According to Captain Ftitterer, of the Memel bark Orion 

 (a petroleum vessel plying between Philadelphia and Ham- 

 burg), during a return voyage with a cargo of the above sub- 

 stance on board, he observed an easterly deflection of the 

 compass amounting to as much as 90. He had been pre- 

 viously informed that such would be the fact, but had been 

 inclined to doubt it. A cargo of railroad iron, brought over 

 by him to Philadelphia from Hamburg, exercised no magnetic 

 attraction. 3 C, August 19, 816. 



IDENTIFICATION OF LIGHTS AT SEA. 



Sir William Thomson, in a series of remarks upon the iden- 

 tification of lights at sea, urges the adoption of a system of 

 indications corresponding to the Morse telegraphic alphabet, 

 so that, by the varied combinations of short and long flashes, 

 a particular number shall be signaled, corresponding to that 

 of the light-house. The result will be that at whatever point 

 the vessel first makes the coast of the country, the locality 



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