392 



" To His Royal Highness Prince Albert of Saxe Cohurg and 

 Gotha, K.G., F.R.S., Sec. 



" The Humble Address of the President, Council, and Fel- 

 lows of the Royal Society of London for improving 

 Natural Knowledge. 



" May it please Your Royal Highness, 



" We, the President, Council, and Fellows of the Royal Society 

 of London for improving Natural Knowledge, beg to be permitted^ 

 on the present occasion, to offer to Your Royal Highness our con- 

 gratulation on the providential escape of Her Majesty and Your 

 Royal Highness from the murderous attack of an assassin. 



" That the same Almighty Arm may continue to preserve Her 

 Majesty and Your Royal Highness from every danger, and from every 

 evil, is our most sincere and earnest prayer." 



June 9, 1842. 



The MARQUIS OF NORTHAMPTON, President, in the Chair, 



A paper was read, entitled, " On the Specific Inductive Capaci- 

 ties of certain Electric Substances." By William Snow Harris, Esq., 

 F.R.S. 



The author, pursuing the experimental inquiry suggested by the 

 theory of Mr. Faraday relative to the differences in specific induc- 

 tive capacity exhibited by different dialectric substances, instituted 

 a series of experiments for determining with precision their compa- 

 rative powers of insulation, and of sustaining by induction charges of 

 electricity. The substances to be examined were cast into the form 

 of circular plates and furnished on both their surfaces with circular 

 coatings of tinfoil of a diameter equal to one-half that of the plate, 

 and the electric intensities were measured by electrometers of the 

 same construction as those which he used in his former experiments, 

 and which he has described in his papers already published in the 

 Philosophical Transactions for 1859. The results are stated in ta- 

 bles ; from the last of which it appears that the inductive capacities 

 of the dialectric bodies tried, that of air being expressed by unity, 

 are proportional to the following numbers : — 



Substances. Relative capacities. 



Air 1 



Rosin 1*77 



Pitch 1-8 



Bees' wax 1*86 



Glass 1-9 



Brimstone 1*93 



Shell-lac 1-95 



The author, in conclusion, offers some observations on the expe- 



