Minerals containing Columbium. 419 



Torrelite and columbite differ in their hardness, that of 

 the former being 4*25, of the latter 6*25. Tantalite and 

 ferro tan tali te are described as hard ; but we know not the 

 exact amount. 



From the preceding observations and analyses, I con- 

 ceive, that no doubts can remain either with mineralogists 

 or chemists, that the four minerals described in this paper 

 constitute four different species. 



Article IV. 



Experiments and Observations on Visible Vibration, 

 By Charles Tomlinson, Esq. 



{Continued from page 20.) 



on the vibration of porcelain and earthenware 



vessels. 



116. The investigation of the vibratory action of vessels 

 of other material than glass has been purposely deferred 

 until now, because, from a few phenomena already alluded 

 to (76), it would seem, that the vibration of porcelain, 

 earthen, and wedgwood-ware vessels is peculiar, and, there- 

 fore, deserving a separate inquiry. 



It has been said (75), that two tones can be produced 

 from earthenware mugs, &c., and Mr. Dodd found that 

 with a common blue cylindrical cup, two notes D and E 

 were produced separately, and alternated four times during 

 one revolution of the finger : that is, there were four points 

 producing D, and four other points producing E. The 

 additional phenomena noticed (75) are not very precisely 

 stated, as the mode of vibration of these vessels, then 

 adopted by Mr. Dodd, **by striking the edge gently with 

 a quill," is a very imperfect one, and not capable of pro- 

 ducing the decisive results, which the judicious application 

 of a well rosined bow effects. I, therefore, propose in this 

 paper, to commence a statement of the results of my 

 inquiry into the vibratory action of vessels of porcelain, 

 china, earthenware, metal and wood. The very curious 

 results which I have obtained, may, probably, be thought 

 sufficiently important to allow me to state them somewhat 

 fully. 



2 E 2 



