22 REPORT — 1839. 



cup, and lifted it out; and, still holding his finger tightly over the 

 mouth of the tube, laid it flat on a table, when the mercury in the tube 

 soon lay at the under side of the tube, leaving the upper part along the 

 length of the tube void. Upon then turning the tube slowly round, 

 still keeping the finger on its mouth, every speck of air was gathered 

 up. He then placed the tube in an upright position, with its mouth 

 upwards, still keeping the finger firmly on ; and, placing a funnel of 

 clean dry paper about the upper part, an assistant filled the funnel with 

 hot mercury, so as to cover the finger. Upon slowly withdrawing the 

 finger, the mercury went gently in, and displaced almost perfectly the 

 atmospheric air which had gathered into the void space. By renewing 

 the process which succeeded the previous washing of the air out of the 

 tube, once, or at most twice, a column of the most perfect brilliancy 

 was obtained. He had mentioned this simple method to Dr. Robinson, 

 of Armagh, who suggested that, to get rid of the damp and greasiness 

 of the finger, it would be better to cover it during the process with 

 clean and dry caoutchouc ; and this was found a decided advantage. 



The method of procuring an invariable surface in the cistern was 

 equally simple. From the imperfection of the author's sight, it was an 

 object of much interest to him to have as few readings or adjustments 

 depending on sight as possible. He proposed, therefore, to divide the 

 cistern into two compartments, by a diaphragm of sheet iron or glass, 

 brought to a sharp edge at top. Into one of these compartments the 

 barometer tube dips ; in the other is placed a plunger of glass or cast 

 iron, which can be raised or lowered by a slow screw movement. To 

 prepare for an observation, the plunger is first screwed down, by which 

 it displaces the mercury in one compartment, and raises its surface in 

 the other above the edge of the diaphragm ; upon raising it slowly 

 again, the mercury drains ofi* to the level of the edge of the diaphragm, 

 thus, at every observation, reducing the surface to a fixed level. 



A letter was received from Prof. A. D. Bache of Philadelphia, on 

 the subject of rain at different heights. It is expected that this and 

 other subjects will be treated of in the Report on the Meteorology of 

 the United States of America, which Mr. Bache has undertaken to 

 draw up for the Association. 



Experiments to determine the Fluency or Viscidity of different Liquids 

 at the same Temperature, and of the same Liquids at different Tem^- 

 peratures. By Dr. Ure. 



The author, referring to a memoir read to the Society of Civil Engi- 

 neers, states a new mode of experiment and gives the results as under. 



Upon this occasion I put the liquid, either cold or heated to a certain 

 temperature, into a glass funnel, terminated at its beak with a glass 

 tube of uniform bore, about one eighth of an inch in diameter, and three 

 inches long. The funnel was supported in a chemical stand, and dis- 



