66 



are propagated is small. When light is plane-polarized, or unpo- 

 larized, that is, when there is no retardation, or the phases of the 

 component vibrations are simultaneous, then the opposite sums de- 

 stroy each other; that is, the number of terms involved is greater, 

 or the sphere of the influence of the force greater. Since both kinds 

 of light can be propagated indifferently through ordinary media, it 

 follov^^s that the sphere of influence of the force, or number of mole- 

 cules taken into accoont, does not here depend on the arrangement 

 of the molecules of ether in the medium, but on the retardation of 

 one of the vibrations behind the other, or the absence of it, origin- 

 ally impressed on the ray in the respective cases. 



A paper was also read, entitled, " An Experimental Inquiry into 

 the influence of Nitrogen on the Growth of Plants." By Robert Rigg, 

 Esq. Communicated by the Rev. J. B. Reade, M.A., F.R.S., &c. 



The author, after briefly alluding to a former paper laid before the 

 Royal Society, describing the chemical changes which occur during 

 the germination of seeds, and some of the decompositions of vege- 

 table matter, proceeds, in the present paper, to trace a connexion 

 between the phenomena exhibited during the growth of plants, and 

 the direct agency of nitrogen. The experiments by which the au- 

 thor supports his views are arranged in separate tables, so drawn out 

 as to indicate not only the quantities of carbon, oxygen, hydrogen, 

 nitrogen, and residual matter, in about 120 different vegetable 

 substances, but also the quantity of nitrogen in each compound, 

 when compared with 1000 parts by weight of carbon in the same 

 substance. The most important of these tables are those which ex- 

 hibit the chemical constitution of the germs, cotyledons and rootlets 

 of seeds; the elements of the roots and trunks of trees, and the cha- 

 racters of the various parts of plants, especially of the leaves, at dif- 

 ferent periods of their growth. From this extensive series, which is 

 stated to form but a small portion of the experiments made by the 

 author in this department of chemical research, it appears that ni- 

 trogen and residual matter are invariably the most abundant in those 

 parts of plants which perform the most important offices in vege- 

 table physiology ; and hence the author is disposed to infer, that 

 nitrogen (being the element which more than any other is perma- 

 nent ''in its character) when coupled with residual matter, is the 

 moving agent, acting under the living principle of the plant, and 

 moulding into shape the other elements. The method of ultimate 

 analysis adopted by the author, enables him, as he conceives, to de- 

 tect very minute errors, and therefore to speak with certainty as to 

 the accuracy and value of every experiment. 



A paper was also read, entitled, " Researches in Rotatory Mo- 

 tion." By A. BeU, Esq. Communicated by the Rev. W. Whewell, 

 M.A., F.R.S., &c. 



This paper, which is altogether analytical, contains several new 

 theorems in rotatory motion, respecting the effect of the centrifugal 

 force arising from a rotation about any axis, in producing rotation 



