.510 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



The sensitiveness of the d'Arsonval galvanometer in measuring 

 steady currents is 9.1 X 10 6 cms. per ampere of current. 



The leakage currents given are, as a rule, near the maximum values, 

 fur most of the currents were slowly decreasing with the time when 

 they were taken. But " Par. B " showed a marked increase of the 

 current with the time. 



O.l per cent. 

 of Free Charge 



COVER GLASS CONDENSER. 



0.0005 



0.0010 

 TIME OF CHARGING. 



0.0015 



Figure 11. (Tables XXXIX and XL.) 



The Condensers of Pure Paraffin Sheets. 



The preparation of thin slabs of pure paraffin for use as the dielec- 

 tric of a parallel plate condenser for experimental purposes has always 

 been a difficult task. Boltzmann recommends that the melted paraffin 

 be poured between two plates of plate glass whose inner surfaces have 

 been coated over with a thin film of oil, in order that the slab may be 

 readily sepai-ated from the plates after it has cooled and become hard. 

 This leaves thin films of oil over both surfaces of the paraffin slab, and 

 these should be scraped off before the slab can be used. The writer 

 made some fairly thin slabs three years ago by pouring hot paraffin 

 into a square frame of wood placed on a single plate of glass lying 

 horizontally and having a film of oil to allow the later separation of the 

 paraffin. But he has never yet seen any paraffin so formed which was 

 free from air bubbles or small cavities. It is possible, and perhaps 



er all the easiest way, to saw off slabs of paraffin from a large block 

 and then to plane down the surfaces, but this will not give very thin 

 slabs. 



