S84< Dr. Daubeny's Lines of Inquiry 



bar in wet clay and not sufFering it to touch the helix, but the 

 effect was still the same. I tried bars of silver, copper, zinc, 

 tin, lead and brass, but no similar effect was produced. 



In three bars of equal sizes, one of soft iron, one of hard 

 steel, and the third a permanent magnet, no sensible difference 

 in these effects could be detected. 



These experiments tend to prove that the particles of a bar 

 of iron, when changing its electrical state, have a tendency de- 

 cidedly motive, and that too along the bar in the direction of 

 its axes. I have not yet been able to prove that any excitation 

 in the same direction will induce an electric current (which I 

 think is highly probable), but have put together these facts 

 in a hurried manner, in order that we may have an opportu- 

 nity of hearing of such investigation as we may naturally ex- 

 pect from the immense amount of talent employed in this in- 

 teresting branch of science. I think also that these facts may 

 serve to elucidate many others which I have not yet heard ex- 

 plained, but must reserve hypotheses for a future opportunity. 



Yours, very respectful!}^, 



Birmingham. J. P. Marrian. 



LXVII. Lines of Inquiry connected 'with the Theory of Agri- 

 culture. By Charles Daubeny, M.Z)., F.R.S., Professor 

 of Rural (Economy in the University of Oxford^. 

 ¥ WILL now conclude by instancing a few lines of inquiry 

 *• connected with the theory of agriculture, which neverthe- 

 less, from their intricacy, as well as from their having no direct 

 bearing upon practice, do not seem of a nature to admit of 

 being properly investigated, except it be upon an experimen- 

 tal farm. 



The first of these relates to the power which plants possess 

 of substituting one ingredient for another, as for example, soda 

 for potass, lime for magnesia. 



On this point we have at present some rather conflicting 

 evidence. Saussure, for example, tells us, that firs from two 

 different soils contain different earthy constituents, although 

 the sum total was as nearly as possible the same ; and Berthier 

 has reported similar results as obtained by himself. In these 

 instances lime seems to have replaced potass, soda and mag- 

 nesia, whilst in other cases an inorganic acid appears to have 

 been substituted for an organic one, as the sulphuric acid in 

 opium for the meconic. 



* Extracted from the author's " Lecture on Institutions for the better 

 Education of the Farming Classes, especially with reference to the proposed 

 Agricultural College near Cirencester, &c. Delivered at the Botanic Gar- 

 den, Oxford, on Tuesday, May 14, 1844." Oxford, 1844, 8vo. 



