362 M. P. Koblrausch on a Variation-Barometer. 



Oceanic Circulation, — as is also Dr. Meyer, who has been engaged 

 for some years in the study of the Physics of the Baltic and the 

 North Sea. 



If Mr. Croll cannot apprehend a Physical conception which 

 such men as Sir William Thomson and M. Dumas (who have 

 kindly allowed me thus to cite their authority) accept as having 

 a valid scientific basis, I submit that the fault is not mine, 

 but his ; and shall not feel called upon to prolong a discussion 

 which will obviously never convince him. My time will be 

 much better employed in working out an experimental investi- 

 gation by which I have reason to hope that further light will be 

 thrown upon the matter. 



1 remain, Gentlemen^ 



Your obedient Servant, 



William B. Carpenter. 



XLVI. A Variation-Barometer. By F. Kohlrausch*. 

 [With a Plate.] 



A BAROMETER which combines with unbounded sensitive- 

 ness the absence of any friction, which requires only a 

 single observation to be made that consumes no time, and pos- 

 sesses so slight a moment of inertia that it follows the variations 

 of the atmospheric pressure in the fraction of a second, will pro- 

 bably excite some interest ; wherefore I will describe the simple 

 way in which I have produced such a one (Plate IV. fig. 3). 



The air-exhausted metal ring from a Bourdon aneroid f is on 

 one side firmly screwed on a holder ; the other, free end pushes 

 with its rounded projection against a small mirror in a metal 

 frame, which is suspended on little steel springs (strips of pen- 

 dulum-steel). An axis, which I first tried, even the finest, ren- 

 dered the sensitiveness illusory; I had therefore put aside as use- 

 less the apparatus already four years old. The mirror-holder can 

 be shifted a little on the bottom-plate by means of two notches ; 

 at the lowest height of the barometer the mirror must rest more 

 securely against the projection. A small wing, soldered to the 

 ring, and dipping deep into the liquid (glycerine) contained 

 in a vessel, serves to rapidly still any vibrations. 



The instrument is set up firmly upon a wall-stand, best by 

 means of a screw through the centre of the bottom-plate/after re- 

 gulating it with the adjusting-screws ; and then the observations 

 are effected in the usual manner with telescope and vertical scale J. 



My scale is placed at about 3 metres distance from the mirror. 



* Translated from a separate impression, communicated by the Author, 

 from PoggendorfPs Annalen, vol. cl. p. 423. 



t I have obtained such tubes through M. Apel, University Mechanician, 

 Gottingen. 



X M. Waibler, Mechanician, Darmstadt, supplies the apparatus for 12 

 thalers. 



