20 REPORT— 1851. 



be readily detected by clear platlna wires connected with a very sensible galvano- 

 meter. Two have been employed, one of 4000 coils, the other of 20,000. The 

 following results have been arrived at by examination of what happens in different 

 sections or the same section of the plant. Since my investigations, some of these 

 results have been confirmed by M. Becquerel in an independent way. 



Electric currents exist in all parts of vegetables, except in those which are furnished 

 with insulating substances, or which contain scarcely any internal humidity. 



These currents exist night and day, in the sunshine as well as in the shade ; they 

 are not destroyed by an exposure to the vapours of aether continued for twenty-four 

 hours, nor by the partial or total separation of the portion examined from the re- 

 mainder of the plant, so long as that portion is not dry. 



In the roots, the stems, the branches, the petioles and the peduncles, a central 

 descending current and a peripherical ascending one are to be found, which may be 

 called axial currents. 



On connecting, by means of the galvanometer, the layers of the stem where the 

 liber and the alburnum touch (and where several botanists admit a descending flow 

 of elaborated sap), either with the more central parts, such as pith and perfect wood, 

 or with the younger bark, a lateral current appears from these layers to the neigh- 

 bouring organs. 



The strength of these currents, as well as of those which are exhibited in the other 

 parts of the plant, depends on the energy of vegetation and the abundance of sap 

 pervading the part under examination. 



A current is also found when any portion of the plant is placed in the circuit of 

 the galvanometer, the other extremity of the wire being inserted in the soil at a di- 

 stance which may be very considerable if the tract is wet. The plant is negative in 

 relation to the soil. 



All these phienomena (the connexion of which with those described by MM. Mat- 

 teucci and Dubois-Reymond is obvious) may probably be explained by the fact, that 

 when two portions of a liquid, acid, alkaline or neutral, the concentration of which 

 is different, are separated by a porous organic membrane, a current of electricity 

 proceeds from the denser to the rarer. 



The electric state of the soil, and perhaps the exhalation which takes place in the 

 organs furnished with stomata, have an influence upon the electricit)' of the ambient 

 atmospheric strata. 



Description of a Sliding Rule for converiinff the observed Readings of the 

 Horizontal and Vertical Force 3Iagnetometers into Variations of Magnetic 

 Dip and Total Force, By John Welsh, Keio Observatory. 



The formulae for converting the observed changes of the two components of mag- 

 netic force into their resultants, dip and total force, are 



, . i sin 2^ /AY AX\ ,AR . ., „ AY , ^ AX 



^'•'=-'^^=(I^^0OO2959V-Y -X )^"'^-R-=^'"^ 5 Y-+^°^^-X-' 



where ^=magnetic dip ; R, the total magnetic force ; X, the horizontal, and Y, the 

 vertical components of force. 



The formula for changes of dip therefore is of the form 

 Angular change of dip=aV— 5H, 

 where V and H are the observed scale readings of the vertical and horizontal force 

 instruments, and a and h certain factors depending upon the dip at the place, and 

 the scale coefficients of the instruments employed. 



In Plate I, fig. 2, let A be a fixed scale representing the variation of dip in 



angular measure ; let e be the adopted length for one minute on the dip scale 



A ; then make a scale B on one edge of the sliding piece, such that one of its 



. . . e . . 



divisions ^ — . Similarly, on the other edge make a scale C, one of whose divisions 



=T-. These scales must be so placed that when the slide is closed the zero points 



of all shall be in a line. Draw also a fixed mark m, in such a position, that when the 

 slide is closed it shall point to the upper extremity of the horizontal force scale C. 



