1835.] Observations on Visible Vibration. 133 



remarkable, the intervals between the notes were observed 

 to lessen in proportion as water was added, so that when the 

 vessel was quite full, the two notes seemed to become uni- 

 sonant. Tea cups of different dimensions produced similar 

 results ; but Mr. Dodd was not attended with equal success 

 when saucers and plates were employed, probably on account 

 of the difficulty of holding them without disturbing the 

 vibrations, the former vessels being held by the bottom rim 

 and not by the handles. 



In repeating these experiments I found it necessary, in 

 order to succeed, to follow Mr. Dodd's directions, and listen 

 for a *' still small voice, " the sounds produced bearing the 

 same relation to musical notes as a whisper does to the voice. 

 The intervals between the notes were never more than three 

 semi-tones, and can be determined by a tolerably accurate 

 musical ear. The eight divisions of the rim may likewise 

 be observed by striking every part of the edge gently with 

 a quill ; at four points a certain note is heard ; at four^other 

 points a higher note, and at the intermediate parts both are 

 heard together : and, indeed, the same will result by striking 

 either the interior or exterior surfaces, as well as the edge. 

 In some instances, there was a difference in the strength of 

 the two notes, which inclined Mr. Dodd to think that one 

 of them might be analagous to a beat in the intervals of the 

 other ; but, in general, the notes were so nearly equal in 

 intensity, that eight vertical nodal lines are supposed to 

 exist, each of which, separates two vibrating arcs which 

 produce different notes. 



Brown Street, Salisbury, Sth July 1835. 



Article VII. 



Purification of pyroligneous acid and manufacture of acetate 

 of lime, according to the method adopted by chemical manu- 

 facturers. By Chr. Phil. Pruckner, of Hof.''^ 



Introduction. — From his first connexion with the manu- 

 facture of pyroligneous acid, which has been on a great 

 scale, Priickner endeavoured to fall upon the cheapest and 

 quickest method of purifying it from the foreign matter 



* Erdmann und Schweigger-SeideVs Journal fur Praktische Chemie, iv. 21. 



