133 On the Construction of Da Luc's Columns. 



derstood from the following figure ; which represents the disks, as 

 compressed, in due order, within a glass tube, by spirals of wire. 



Each of the wires of which these spirals were formed, at the ends 

 enclosed in the tube, being unaltered throughout the remaining por- 

 tions of their length, were passed through corks closing the orifices 

 of the tube. The series thus prepared, is to be placed in the situa- 

 tion of the electric column, appended to the instrument agreeably to 

 Fig. 1, being in like manner suspended from the rods outside of the 

 vessel by means of the projecting wires already mentioned. Thus 

 situated, if there be any adequate degree of electromotive power in 

 the series under trial, and the atmosphere sufficiendy dry, the excite- 

 ment of the poles will be communicated to the knobs, and be indica- 

 ted by the consequent vibrations of the gold leaf, suspended between 

 them. 



When a larger series is used, such as that represented at DD, 

 Fig. 1, the vibrations will be discontinued, only in consequence of 

 the adherence of the leaf to one or the other of the knobs. This adhe- 

 rence usually ceases, on touching with a finger the little brass ball at 

 the vertex of the instrument, to which the forceps holding the leaf is 

 affixed. The finger being removed, vibratory pulsations will recom- 

 mence, to be sooner or later arrested in the same manner as at first. 



When duly connected with the poles of a voltaic battery, of seven 

 hundred pairs, excited merely by pure water, the pulsations of the 

 leaf are quick and incessant. It serves in this way to indicate the 

 electric intensity, but does not furnish any criterion of the divellent, 

 igniting, or electro-magnetic powers of a voltaic series. 



It may readily be perceived, that the electrometer, constructed as 

 herein described, constitutes an electrical indicator, which may en- 

 able us to discover the electromotive powers of various substances 

 arranged as disks in a series, or as coatings to disks. I have already 

 ascertained that aurum musivum spread on the naked surface, of the 

 tinned paper produces an electromotive series. 



The piling of the disks was facilitated by using a punch excava- 

 ted so as to leave a point in the center, by which the center of each 

 disk was punctured. By means of the puncture thus made, it was 

 easy, even for an unskillful operator, to string them concentrically 



