468 Intelligence and Miscellaneous Articles, 



thought immediately struck me that its warmth must be due to the 

 air enclosed within it ; and if such were the case, it should have a 

 temperature intermediate between that of the water and the air. 

 And such really was the case ; for the air, though feehng very cold 

 in consequence of a strong easterly wind blowing, did not fall 

 below 50° F. 



I may state that the phsenomenon appearing to me very curious at 

 the time, considerable care was devoted to the observation of these 

 temperatures, the thermometer being allowed to remain long enough 

 in each medium to become quite stationary. 

 I am. Sir, 



Yours respectfully, 



Henry M. Witt, F.C.S., 

 Assistant Chemist to the Government 

 School of Mines. 



[I have a strong impression that the temperature of the foam in 

 my case was much higher than that of the air. I, however, judge 

 from my feelings merely, and I know that these are liable to error. 

 A small india-rubber balloon, for example, held in the hand feels 

 warm. — J. T.] 



DESCRIPTION OF A NEW BAROMETER. BY M. DAVOUST. 



This barometer is founded on the following principle. Suppose 

 a cylindrical glass tube, in a vertical position, containing a small 

 column of mercury, and of which the extremities may be opened and 

 hermetically closed at pleasure. Let S be the upper and I the 

 lower extremity ; the column of mercury is in contact with S, 

 which is closed. I is at first open, then reclosed ; S is opened : 

 the mercury sinks in small quantity. When it has again acquired 

 its position of equilibrium, S is again closed and I opened : a fresh 

 sinking of the mercury takes place. I give the name of operation 

 to the successive opening of the upper and lower extremities. The 

 fall of the mercury at the end of the first operation, is a function 

 of the atmospheric pressure ; but this fall is too small to enable us 

 to judge with sufficient exactitude of the pressure of the external 

 air. To remedy this inconvenience, the same operation is repeated 

 until the mercury arrives as close as possible to the extremity I; the 

 total fall of the mercury may then be measured with sufficient ex- 

 actitude to enable us to judge from these variations, as well as from 

 the number of operations performed, of the variations of the atmo- 

 spheric pressure. Such is the fundamental idea of the barometer 

 which I call the repeating barometer. 



It consists essentially of a graduated glass tube, furnished at its 

 two extremities with valves kept closed by a spring, and which may 

 be opened by means of a kneed lever. But to make use of the 

 instrument there are some essential conditions to be fulfilled, and 

 this is the purpose of the construction which I describe in detail in 

 my memoir. Thus the caoutchouc forming the valves does not bear 

 immediately upon the large glass tube, for some drops of mercury 

 might remain adherent to it, which would render the observations 



