Use of Gutta Percha in Electrical Insulation. 297 



and kneaded for some time between the fingers, as if with 

 the intention of dissipating the moisture within it, it becomes 

 as good an insulator as the best. 



" I have soaked a good piece in water for an hour nd on 

 taking it out, wiping it, and exposing it to the air for a minute 

 or two, found it insulate as well as ever. Another piece was 

 soaked for four days, and then wiped and dried ; at first it 

 was found lowered in insulating power ; but, after twelve 

 hours' exposure to air, under common circumstances, it was 

 as good as ever. I have not found that a week's exposure 

 in a warm air cupboard, of a piece that did not insulate, 

 made it much better : a film on the outside became non-con- 

 ducting ; but if two fresh surfaces were exposed by cutting, 

 and these were brought into contact with the electrometer 

 and the finger, the inside portion was still found to conduct. 



" If the gutta percha, in either the good or the bad condi- 

 tion (as to electrical service), be submitted to a graduall}' in- 

 creasing temperature, at about 350" or 380', it gives off a 

 considerable proportion of water ; being then cooled, the 

 substance which remains has the general properties of gutta 

 percha, and insulates well. The original gum is probably 

 complicated, being a mixture of several things ; and whether 

 the water has existed in the substance as a hydrate, or is the 

 result of a deeper change of one part or another of the gum, 

 I am not pi'epared to say. All I desire, in tliis note, is to 

 make known its use in the arrangement of extemporary or 

 permanent electrical apparatus for the advantage of work- 

 ing philosophers, both juvenile and adult." 



Communications respecting Scandinavia. In a letter from 

 Hekr Karl Bruj^jer Jun., to Professor Studer. 



On the 1st of December 1845, says Prof. Studer, Ilerr 

 Bruner wrote me from Berlin the following amongst other 

 matters : — 



Having arrived from my northern (our, it is not only 

 my duty, but 1 liave also great pleasure, in giving you an 

 answer to the letter which I had received shortly before my 

 departure. 



