Dr. Chowne on the Movement of Atmospheric Air in Tubes. 229 



Similar comparative observations, with the hygrometer placed at 

 the upper aperture of the tube (fig. 2), yielded similar results. 



In these experiments the lower extremity of the vertical tube was 

 bent thrice at right angles*, for convenience in making the obser- 

 vations, and it appeared desirable to ascertain what influence the 

 long branch of the siphon-like tube had in the production of the cur- 

 rent. For this purpose the long vertical tube (fig. 3) was made 

 moveable at A, so that the apparatus could be alternately converted 

 into a siphon with equal limbs 4 inches in length (fig. 4), or one 

 with a short leg of 4 inches, and a long one of 9G inches (fig. 3). 

 In twelve observations, when the long leg was inserted, the mean 

 depression of the hygrometer was 2°'5 Fahr. ; when the limbs were 

 of equal length, 2"-25 Fahr. 



Considering it possible that the current of air existing in the tube 

 might have sufiicient force to move a light body delicately suspended 

 in its track, an elbow.E (fig. 5), was inserted into the upper orifice of 

 the tube, to which a piece of glass tube, G, of the same diameter, was 

 adapted, 6 inches in length, and a disc of tissue-paper, weighing one 

 grain, which nearly occupied the area of the tube, was delicately sus- 

 pended by a hair, at right angles to the axis of the tube. A slide valve 

 was so adapted to the lower orifice, that this aperture could be opened 

 or closed without entering the room. The air of the room being qui- 

 escent, it was found that when the slide valve closed the lower orifice 

 of the tube, the disc of tissue paper remained perfectly quiescent ; 

 but that when the slide valve was withdrawn, leaving the lower 

 orifice open, oscillations of the paper occurred, and it was projected 

 Fig. 5. Fig. 6. 



zinr\ 



V. Slide valve. D. A disc vrhich occupies nearly 



the vphole area of the tube. 

 * The tubes used in these experiments were bent either at their lower or upper 

 extremities for convenience merely. 



