463 



affected by the change. This explains why the readings of the dif- 

 ferential thermometer varied from 33'0 to 33- 5 as described in the 

 paper, without producing a corresponding change in the velocity of 

 the anemometer. 



For the purpose of obtaining a more correct estimate of the 

 influence of a given increase of heat within the tube, the author 

 introduced into the tube at its lowest extremity, a phial containing 

 eight ounces of water at the temperature of 100 Fahr., corked so 

 that no vapour could escape. The result showed that in thirteen 

 observations a quantity of heat equal to an increase of one-tenth of 

 a degree on the scale of the differential thermometer, was equivalent 

 to a mean velocity of the anemometer of 3*6 revolutions per minute, 

 the greatest number being 3*8, the least 3 '3 per minute. 



These observations render it still more evident, that if a higher 

 temperature within the tube had been the main cause of the revolu- 

 tions of the anemometer, the variations in their velocity would not 

 have been in such exact relation to the elastic force of the atmo- 

 spheric vapour, as has been shown to be the case. They also lead 

 to the inference, that the apparent excess of heat within the tube 

 alluded to by the author in his Paper read before the Society in 

 1855 did not really exist, and to the conclusion that, if such excess 

 had been present, the anemometer would not have been brought to a 

 state of rest by depriving the air of the room of a portion of the 

 moisture ordinarily suspended in it. 



II. "On the Relation between Boiling-point and Composition in 

 Organic Compounds." By HERMANN KOPP, Esq. Com- 

 municated by Dr. HOFMANN. Received March 20, 1860. 



(Abstract.) 



The author was the first to observe (in 1841) that, on comparing pairs 

 of analogous organic compounds, the same difference in boiling-point 

 corresponds frequently to the same difference in composition. This 

 relation between boiling-point and composition, when first pointed 

 out, was repeatedly denied, but is now generally admitted. The con- 

 tinued experiments of the author, as well as of numerous other 

 inquirers, have since fixed many boiling-points which had hitherto 

 VOL. x. 2 K 



