IMPROVEMENTS IN THE ELECTRICAL MACHINE, fl 



them; no light is now visible in the dark, and the negative 

 power seems fully equal to the positive. 



The rude sketch, PI. I, fig. 5, will give some idea 

 of the manner of fixing the handle with its disc. A brass cap 

 is fitted, by grinding, over the inner nut and screw before 

 cementing, to preveut their being fixed by the cement. It 

 also serves as a reservoir. P. COPLAND. 



Observations on Mr. Copland's Paper. 



The machine described in the Professor's paper was not The improve- 



oriirinallv made for hirn, but for a gentleman who employed m<mt had been 



© • o r j employed tx> 



it principally for his amusement. I did not therefore at- fore, 

 tend particularly to its construction with regard to the per- 

 fection of either the positive or negative powers, and they 

 might be imperfect. The Professor appears to think, that 

 the greatest imperfection was the insulated winch which im- 

 perfection he has overcome by the application of a disc 

 This disc is precisely similar to an invention of mine made 

 about 30 years ago, when I resided in Holland. I have given 

 a description and plate of it in the second vol. of my 

 Eigenshappen der Electriciliet, printed at Amsterdam, 1782; 

 but on account of its awkward appearance, and risk of 

 breaking, I left off using it, and have since employed asim- but disused. 

 pie insulated winch, placed at a greater distance from the 

 mahogany pillar of the machine, and this I find a more per- 

 fect remedy. 



With respect to the other improvements the Professor Farther re- 

 imagined he has made, and proved by experiment; I am in- ^ect^n'uil- 

 clined to think he has been deceived, because the negative tion, 

 part of an electrical machine, with such imperfect insula- 

 tions as he describes, will charge a phial to a certain degree, 

 with the same number of turns as one with'the most perfect 

 insulation. Such imperfect insulation does not begin to act 

 till the charge attains a certain degree of intensity, till then 

 it keeps pace with the charging power of a machine perfectly 

 insulated. Tins circumstance does not seem to have oc- 

 curred to the Professor ; had he thought of measuring the 

 advance of the charge at each revolution, before, and after, 

 he had finished his alterations, the result would have been 



more 



