744 Transactions of tee American Institute. 



applied immediately and well rubbed on; the result is a highly 

 sensitive coating of mercury which will seize any particles of gold 

 passing over it. In the pans the cyanide is applied with each 

 charge of mercury. 



A NEW TELEGRAPHIC THERMOMETER. 



Prof. Wheatstone has devised a new thermometer, which by 

 breaking and closing an electric current will convey its record to 

 distant places. The same principle is applicable to the whole class 

 of meteorological instruments. The telegraphic thermometer con- 

 sists essentially of two parts. The first is the magnetic motor, 

 constructed on a plan similar to that used by the inventor m his 

 alphabetical magnetic telegraph, and is so arranged that by turn- 

 ing a handle the lever at the other extremity of the line \n\\ 

 describe, by regular steps, a complete circle. The second part con- 

 nists of a metallic thermometer, in which the unequal expansion of 

 two different metals is made to move a lever or pin around a gradu- 

 iited circle, which marks the degrees of temperature. The two 

 parts are in such proximity that the telegraphic lever in passing 

 firound the circle must, at some point, come in contact with the pin, 

 which is moved by means of the expanding or contracting metals. 

 This contact breaks one circuit and completes another, and thus 

 Iransmits to the other extremity of the telegraphic line information 

 of the particular degree of heat at that instant indicated by the 

 thermometer. The uses to which this telegraphic thermometer 

 may be applied are, among others, the following: The thermometer 

 may be placed on a high mountain, and in a place not easily 

 accessible; for instance, on the highest point (»f Mount Blanc, and 

 in the valley of Chamouni, may be fixed the battery and terminal 

 wires, at which point the interrogator may, from time to time, ascer- 

 tain the temperature at the top of the mountain. In the same 

 manner reports of temperature may be obtained from any point 

 beneath the surface of the eai'th at which the thermometer is 

 located. This thermometer is not self-recording; it responds only 

 when questioned by the operator of the telegraph. 



TEST TOR FIXED AND VOLATILE OILS. 



Mr. Bruce Warner read, before the British Association, a paper 

 "on the electrical resistances of the fixed and volatile oils,'' in 

 which he shows that difference of resistance will indicate the purity 

 of the oil under examination. The process is founded on the dis- 



