Sir W. Harris on some new Phenomena of Residuary Charge. 489 



nexion with the inner coating of the jar. The intensity or attractive 

 force of the residuary or remaining charge is now noted, but as this 

 force is necessarily small, it is taken with the attracting plates at a 

 diminished distance from *1 to *3 of an inch or more, as the case may 

 require, and subsequently reduced to the standard distance of one 

 inch, taking the force to vary, as demonstrable by the electrometer, 



as — - a . This being determined, the relative quantities of electricity 



in the full charge and the residual charge will be as the square roots 

 of the respective attractive forces or intensities ; the total force, as 

 also demonstrable by the instrument, being as the square of the ac- 

 cumulation. Let, for example, the quantity of charge communicated 

 to the jar be 100 measures, and the attractive force, or intensity at 

 distance one inch, be 144 degrees, and suppose intensity of residual 

 force at the same distance='08. In this case we have the simple 

 proportion 100 measures : x measures : : \/l44 : V^OS : : 12 : *283 



and quantity of residual electricity = — = 2*35 measures 



nearly ; so that of the original 100 measures of charge communicated 

 to the jar, rather more than Jfrth remains undischarged in this case. 



The author here offers some explanatory observations on the rela- 

 tive dimensions and extent of coating of the unit of measure and the 

 relative value of the measures quoted, and he thinks if electricians 

 would agree to recognize a standard instrument of this description, it 

 would be attended with very considerable advantage, as in the case of 

 other standard instruments. The unit of measure he employs ex- 

 poses about 9 square inches of coating ; it is about 4 inches long, *8 

 of an inch in diameter, and -^th of an inch thick ; distance of ex- 

 ploding balls "05 of an inch. Similar observations were applied to 

 the thermo-electrometer, the ball of which is 4 inches in diameter, 

 and has a wire of platinum through it of *01 of an inch in diameter. 

 The dimensions of the attracting discs of the hydrostatic electrometer 

 are also noted, which in these experiments were 4 inches in diameter ; 

 the suspended disc weighs 82 grains. The discs are carefully gilded ; 

 5 degrees of the arc of measure represents a force of 1 grain, that is 

 to say, a weight of 1 grain added to either side moves the index 

 5 degrees of the scale. Having offered these preliminary remarks, the 

 author proceeds to the following experiments : — 



Experiment 1. — Variable charges, amounting to 50, 100, 150 

 measures, were successively accumulated on different jars, exposing 

 from two to six square feet of coating, and the residual charges due to 

 each noted ; these were found to be as the total charge. Thus the 

 residual charge for 1 00 measures was in every case double that for 

 50 measures. 



In a succeeding Table are noted — measured charge ; exploding 

 distance ; intensity at distance 1 inch ; residual measures and thermo- 

 electric effect of discharge. It appears by this Table that residual 

 charge is as the total charge ; exploding distances, as the quantity or 



