362 Mr. C. Tomlinson on the Motion of Vapours 



a day, together with, the temperature and the state of the weather. 

 The dew was of the most varied character in the different bottles : 

 in some it was fine, in others coarse ; and the deposit was also fre- 

 quently ploughed into furrows by the weeping tears which trickled 

 down as the moisture on the inner side of the shoulder of the 

 bottle became overcharged. It was beautiful to see the almost 

 clocklike regularity with which the deposits oscillated between 

 the front and back of the bottles. At 9 a.m., when the first 

 observation was generally made, the deposits were on the side 

 nearest the window, often occupying exactly one-half of the 

 bottle; at 3, 4, or 5 p.m., when the second observation was 

 taken and the bottles had been exposed to the sun some time, 

 the deposit was on the furthest side. When the afternoon was 

 cloudless, the bottles were filled with vapour ; but as the evening 

 advanced, the deposits were made on the furthest side, again to 

 pass over to the nearest side as the cold of night was felt. 



With respect, however, to the texture of the dew, the results 

 were anomalous. After several weeks' observation I was not in 

 a condition to place my finger on any one bottle and name its 

 contents frOm the character of the aqueous deposit — except per- 

 haps in the case of carbonic acid, which declared itself by its 

 superior solubility. Suspecting that the bottle's, although new 

 from the glass-warehouse, were not clean, I washed out other 

 similar bottles with strong sulphuric acid, rinsed them with clean 

 water, and filled No. I. with air, No. II. with hydrogen, and 

 No. III. with carbonic acid. On placing these near the window, 

 the results were certainly such as to justify the conclusion that 

 the deposits of moisture are similar in various gases if the re- 

 ceiving surface be chemically clean. In such case, however, we 

 get, not dew, but a sheet of water marked by weeping tears, but 

 without furrows ; and it is often difficult to distinguish on which 

 side the deposit is made, so regular is the watery film. There 

 can be no doubt, however, as to its being deposited on the 

 colder side. 



But if vapour of water in different media presents similar 

 phenomena, different vapours in the same medium give varied 

 phenomena. I have arranged in the window, as nearly as pos- 

 sible under similar circumstances, clean 8-ounce phials contain- 

 ing small quantities of alcohol, ether, benzole, belmontine, bisul- 

 phide of carbon, &c. The deposits varied in texture according 

 to some law depending partly on the varying cohesive force of 

 the liquids in question, by which they form drops of different 

 sizes from the same aperture, and ascend to different heights in 

 capillary tubes of the same bore. 



I may here be allowed to refer to one of Dr. Draper's experi- 

 ments, in which the inside of a glass bottle being marked with a 



