OF ARTS AND SCIENCES. 245 



small condensers, of ten slieets each, to find the comparative insula- 

 tion of various kinds of paper. I put tlie condenser to be tested under 

 pressure, and connected it in circuit with a buttery of four gravity 

 Daniell's cells and a mirror galvanometer. The throw of the uee,dle 

 was disregarded, and the permanent deflection due to the current 

 through the galvanometer and condenser was read. 



Papers. Deflections. 



Pulp (news) 1.0 



Book, glazed, 0.3 



Bond, glazed, 2.05 



Bond, unglazed. No. 18 1.95 



Bond, unglazed. No. 21 1.30 



Tissue, brown coujmercial paraflBne 1.20 



This test showed that the cheaper kinds of paper were better than 

 the bond and that the commercial paraffine was no better than ordinary 

 clean paper. 



A more careful experiment was made to see which of the three 

 chief kinds of paper gave the best insulation. Condensers were made 

 of pulp, pure rag, pure linen, bond (mostly linen), and of Ravelstone 

 writing paper (rag and linen). Each contained ten sheets (21.5 X 

 34.5 cm.) with tinfoil (12.6 X 30 cm,). Four gravity cells were used. 

 The galvanometer was much more sensitive than the one used in the 

 experiments given above. 



Papers. Deflections. 



Pure linen (mean) 43.7 



" " (several hours later) 59.0 



I?ag 6.0 



Eavelstone writing 11.25 



Pulp (news) 4.6 



Manilla 17.5 (?) 



Bond 58.0 



This last deflection gradually increased till it was " off scale." 

 Three days later, with the same galvanometer and condensers, but with 

 fresh gravity cells, an even more conclusive test was made. The condenser 

 made of ten sheets of the commercial parafline paper, used in the sec- 

 ond condenser described above, gave a violent deflection " off scale." 



Papers Deflections. 



Bond . '. 81.0* 



Pure linen 50.5 t 



Ravelstone writing 21.0 t 



Rag 118 



Pulp 3 6 



* Then the deflection slowly crept " off scale " 



t The deflection crept from 22 to this point, where it was still increasing. 



} This deflection crept from 10 upward in a few minutes. 



